oops yeah that is a pretty glaring omission ...have gone back and added some notes and a link to more detail.
 
Thanks Jasyn!



General - Events
Apart from 'random encounters' focussed on monsters, or terrain-based hexmap rules, or treasure generation,games may have various forms of event randomization.

The most developed system for this may be the Mythic RPG designed as a GM 'emulator'; this has a system where a GM is replaced by common-sense question resolution tables- players choose specific questions, assign a probability, and roll. Any roll has a chance to trigger a random event (base system is d100, and doubles less than the 'chaos factor' trigger i.e. chaos factor 3 = 11,22, or 33 will trigger).
In other systems, 'Everway' cards can be used as an idea generator for the GM.
Outside RPGs, the boardgame Tales of the Arabian Nights is slightly interesting too - this uses a huge 'choose your own adventure' type book to generate events rather than using GM fiat (or player fiat as in Mythic).
Magic fumbles ('wild surges' in 2E, or original Advanced Fighting Fantasy's Oops! table, or in Arduin) are also event generators of a sort, although very specific. Most use fixed tables of results (some wild surges have results dependent on the original spell, such as reversed effect or changed target).

The Daredevils RPG has a "Doctrinal Progress" table, which can be rolled on by the GM when an adventure 'has bogged down': an NPC reaction roll is used (abstractly rather than necessarily being NPC reaction) and gives either a 'debacle', setback, or obstacle (...i.e. something happens at least, albeit bad), no progress, chance of data (ie. clue), or advancement/breakthrough.

Adventures/Events may also hinge on NPC organizations.
Justin Alexander has this note here on a "Push Pyramid" for managing NPC organizations:

QuoteBlowback is a lesser known game by Elizabeth Sampat, but it created the Push Pyramid for managing the responses of large NPC organizations to PC activity. Kenneth Hite took this idea and turned it into the Vampyramid for Night's Black Agents, added the Conspyramid for running NPC conspiracies, and then laced in a ton of really cool and innovative mechanics by which the PCs can navigate through these structures.

 
By default, most games have a single attribute for social interaction (Charisma or Appearance or similar), that skills are based off. Games may allow social skills to affect NPCs and not PCs, or PCs may be wholly player controlled.
Social rolls may usually be opposed by a target’s own Charisma, by the game’s Willpower statistic, or may have a set target number (e.g. for 3.x D&D Diplomacy checks, which tended to break since check bonuses could escalate infinitely against the set difficulties by target attitude).
 
 
Games Without Charisma
In other cases, games lack a Charisma but roll functions of it into another attribute (perhaps avoiding having a Cha so player’s can’t dump it):
 
*GURPS bases social skills off Intelligence (which also includes perception and willpower), and may modify the score with advantages/disadvantages.
 
*Savage Worlds bases Persuasion off Spirit (the willpower attribute) though it also has a derived attribute called Charisma which is the sum of persuasion modifiers due to Edges or Hindrances (default 0).
 
*Cortex uses Willpower (e.g. in Supernatural). As well as their Willpower + Persuasion roll (both rated d2 to d12), especially pretty characters may add an 'allure' advantage die (rated from d2 to d6).
 
*Marvel Super Heroes has a Popularity rating which is used for social interactions with NPCs (not a true attribute), which for bad guys is negative (e.g. Galactus, who eats planets, has a popularity of -1000; good for intimidating people but bad for getting dates). This may rise/fall as a result of a character’s actions, or bad press (Spiderman). Being narrowly defined, this was somewhat less prone to abuse compared to the Charismas of other games. (The idea of “negative Charisma” also appears for monsters in Tunnels and Trolls). Villains and Vigilantes still has a Charisma attribute, but it may be increased by donations to charity or good deeds.
 
*World of Synnibarr has a reaction modifier determined by Ego (Int+Wisdom), plus a randomly-rolled personality modifier (rerolled every few levels) and appearance modifier. It also applies a modifier based on differences in alignment (aura colour).
 
 
Games Without Social Checks
In some cases, games may not use mechanical testing of Charisma or social skills – it may be up to the player to talk through any and all situations. Here playing a stinky dwarf with 8 Charisma places a roleplaying hindrance on a character (similar to playing a low Intelligence), rather than providing a penalty to dice rolls. E.g.
 
*older D&D leans towards this approach; though reaction rolls/Charisma checks may sometimes be used, it tends to be less common. The “Etiquette” skill of 2nd Ed. provides knowledge of customs/forms of address to assist in roleplaying, but has no direct effect.
 
* Dragon Warriors has a Looks attribute only (no mechanics are given to test this);
 
*Palladium deliberately eschews social skills. A character has Mental Affinity and Physical Beauty attributes which largely just provide only a guideline on how to roleplay the character; if quite high (>15) a rating gives a “%trust/intimidate” or “% charm/impress” value. (For some further discussion on social skill overuse and Palladium see the RPGPundit thread here: http://www.therpgsite.com/showthread.php?t=20381 )
This can get 'weird'. The "Wu Shu T'Sung" martial art in Ninjas and Superspies for example has a display kata which 'doubles the number of attacks per round, but can't be used in combat' and is 'often enough to intimidate opponents into retreating'. [No mechanics given - an NPC has to be assumed to not know its useless in combat].

 
*Possibly Amber also falls into this category (?)
 
(There's some discussion here by Arminius regarding some of why social checks differ from other checks, that may be of interest. There are also argument's that mechanical testing of charisma is good because this allows characters to have essentially different abilities to the player, if you want to have a character that is persuasive when you're not a used car salesman yourself. Gamers are somewhat split between feeling that use of player skill here is unfair - and that it is the game.)
 
Games With Multiple Social Attributes
*a number of games have separate physical appearance and mental Charisma stats (Palladium, Kult). The Storyteller system has separate scores for Appearance, Charisma and Manipulation, each used in different circumstances, presumably since the game is intended for social interactions to be front and centre such that a single attribute would be overpowered.
 
*Amazing Engine has separate attributes for Charm and Position (social status). "Position" can be checked game mechanically, but seems to convert from 1-100 to a real rank pretty badly; for instance, Bughunters uses a roll of [d100+Pos] to determine a character's background, then that can apply ad hoc modifiers to how character is treated, as well as giving a bonus to a characters chance of a 'job opening' for a given 'class', then with Pos score + a huge bonus by class determining military rank (Position modifies actual rank only slightly since its 1-100 and class can add +0 or +200 etc.).


 
*DC Heroes has three stats, used simultaneously for social rolls. Influence determines how high a roll is needed to affect a target, Aura determines how much effect a character gets if they do succeed (in result points), and target Spirit resists. A few special social interactions use other stats e.g. Force (Str), Weardown (Will) and Bluff (Int).
 
*Harnmaster has various very specific stats including separate Comeliness and Voice attributes and a spiritual “Aura”; social skills (on d%) are each modified for 3 different stats e.g. Acting = Voice/Agility/Intelligence, Languages and Rhetoric are Voice/Int/Will, and Singing is Voice/Voice/Hearing.
 
*The Demonspawn gamebooks have separate scores for Charm or same-sex charisma, and Attraction, or appeal to the opposite sex (the weird thing about those stats in the books were that both attributes added to Life Points i.e. helped absorb damage; Life Points equalled the total of all the characters 8 or so more-or-less percentile [2d6x8] attributes, giving PCs hundreds of LPs).
 
 
Other elaborations
 
*Dying Earth has no attributes, but Persuasion and Rebuff appear as (mandatory) skills. Each of these has a default “Style” which may be rolled (for bonus points) or just selected: Persuade styles are Glib, Eloquent, Obfuscatory, Forthright, Charming, and Intimidating, while Rebuff styles are Obtuse, Wary, Penetrating, Lawyerly, Contrary and Pure-Hearted. Each style is “trumped” by one opposing style, giving it a penalty e.g. Obtuse trumps Glib (they can’t follow what’s being said) but is trumped by Intimidating, or Eloquent trumps Contrary but is trumped by Wary. (see quick start rules: http://www.dyingearth.com/downloads.htm )
 
*Indie game Dogs In The Vineyard is a system designed primarily around a social conflict mechanic. Combats escalate from social to physical; dice are rolled initially then act as a resource during a conflict; a character puts forward dice, with the opponent having to match the roll. A character failing social conflict can “escalate” the conflict, rolling extra dice for weapons/physical stats to continue the exchange; the social layer happening first will always (IIRC) add its resources to the physical combat. Character relationships are worth extra dice.
 
*Exalted has a fairly detailed social combat system including various “Charms” with social effects – many of these very strong. Existence of these may give PCs an incentive to avoiding talking to NPCs, to prevent them being owned immediately.
 
*there's some discussion here on social 'weapons' and 'armour' for FATE, mirroring normal weapons' role but in social combat e.g. a bad reputation inflicting more 'harm', or 'unpopular in particular area' being a social 'consequence' taken rather than 'stress'.

* The Soothsayer RPG has a single Personality (i.e. Cha) rating which also determines points to spend across five personality ratings scored 1-10 (Conscience, Culture, Humanity, Spirit, and Temperament).
 
*Pendragon has a system of Passions (personality traits) rated 1-20 which influence character behaviour. Potentially these model a character’s behaviour and thus their resistance to certain social attacks much more accurately than would a simple Willpower roll or the like e.g. Seduction might actually involve a check against Chaste/Lustful, or Intimidation a check vs. Valorous/Cowardly.

*Supers! (Hazard Studios') treats "Rage" (the disadvantage, e.g. for sample villain 'Ares') as a susceptibility to social combat, suffering "double normal Composure damage from insult-based Presence attacks", berserking at 0.

*HERO is unusual in that "presence attacks" use a mechanic similar to damage rolls (d6 per 5 PRE points as a pool) instead of the default mechanic for success/failure attribute checks (3d6 roll under 9, +1 per 5 stat points)

*Apocalypse World has a weird 'Hx' (History) system where characters have +0 to +3 or so ratings for every other player character, describing the strength of their relationship. These go up and down, modified by use of class-specific sex powers (!) and other events. These are also used in character advancement.
Dungeon World has (at least, in sourcebooks e.g. Class Warfare's) abilities ("Heart of Gold") which if used on PCs cause them to get awarded ('Mark') xp.

*Maelstrom has a slightly interesting trading system. Character stats are rated as percentages; a Trader (only) can make a Persuasion save to sell goods. Each attempt to sell costs d6 time units, with the day of trading having time units equal to the Speed percentage (i.e. Speed as well as running and the like also lets them socialize/sell faster).
It has Preaching rules that distinguish between subjects that have no opinion (successful roll-under preaching ability will do) and actively hostile listeners (who also get a roll under Will to resist).

Existence of social systems (do we roll dice, RP this out, or both?) is something that's fairly divisive among gamers, with their being a tendency for people to run a game in their preferred mode (if possible) regardless of the actual rules. In some cases this leads to a social attribute or skill investment becomes wasted points, when it would've been better for an official rule change removing the options at the outset. This problem happens to not occur somewhat in more abstract games, where it is difficult to separate 'social' tasks from other tasks, due to skills or personality traits or aspects all being useful for whatever (e.g. Marvel Heroic ? perhaps Apocalypse World) - perhaps corresponding to 'intent-based' rather than 'task-based' resolution.

Edit note: I've had some recent interesting offline discussion on social skills, with it being proposed that to use game mechanics, but keep roleplaying, that a player rolls and then has to roleplay the success or failure. I could see talking in character as being something that could possibly end up being skipped as it doesn't affect the roll, but it could be encouraged if the player is rewarded with XP for good roleplaying (i.e. that's accurate to their character).

Different interaction scenarios may just have different rules, or may be defined separately in such a way different resources are involved to purchase them - Storyteller's Appearance vs. Manipulation attributes, 3E D&D's "Diplomacy" and "Bluff" skills. In that case a character may be very good at one thing and poor at another. Dungeon World is interesting in that it has one especially generic manuever for talking - "Parley" can include either and just requires "leverage" over an NPC, which could be a positive incentive (I give you this thing) or negative (Intimidate).

Equipment is purchased in two or three main ways:
 
*Defined currency and expenses: e.g. you get 10 gold pieces; at the inn you spend 3 gold pieces, leaving you with 7 gold pieces. Even in these systems, minor expenses are sometimes assumed to be part of general living expenses, with a character’s living standard deducting a certain number of gold pieces.
 
*Abstract Resource ratings e.g. you have a Resources of two dots, which gives you a OK house/car/etc and an approximate salary. Some games like this rely on fiat to function, while others may list appropriate items for a given resource level, or a check may be made to purchase an item; a character may have a limited # of checks allowed per week or month. Storyteller, DC Heroes, Marvel Super Heroes all have various Resources/Wealth systems that work like this; Call of Cthulhu includes a “credit rating” skill.
The abstract method cuts down on book keeping, but works best where a characters income is generated off-camera i.e. where characters work in a secret identity or have investment funds. It is nonideal for games where a primary objective of adventuring is to earn cash/treasure, e.g. D&D or Cyberpunk.
While it simplifies bookkeeping, systems such as this are also more prone to theoretical breakage e.g. D20 modern's system lets you buy and sell items to potentially increase your Wealth rating, as well as providing potentially unlimited supplies of useful mundane items (such as medikits in Gamma World 5th edition).
 
*Some games are almost a hybrid of these two; characters may have a Resources rating which gives characters an income that they spend to purchase items (GURPS ?). i.e. no resources check system governs what is purchasable, so that conversion to a cash value is necessary anyway.
 
*Character Points: Also as mentioned earlier, some games primarily use character points to purchase important equipment, based on utility. The old joke goes that for Hero a towel might count as power, built as ...
Towel : Transform 1d6 minor (10) wet object to dry, OAF (-1), Extra Time/ Full Phase (-1/2), 2 Recoverable Charges (before towel gets soaked, recover by wringing, -1), No Range (-1/2); Real Cost: 2 points
(Note that Hero does include a disclaimer that very basic equipment should not be assessed a point cost).
 
Elaborations/Variants
*As well as cost, items may have other limiting factors, e.g. “Availability codes” determining if they are legal/illegal. Other games may define regional availability i.e. % availability in a small village vs. a city or castle (Dragon Warriors does this as a percentage; 3.x D&D handles it via a “gold piece limit” by community size)
 
*In Ninjas & Superspies or StarCluster, available equipment depends on the sponsoring organization, possibly built by the GM and/or players using points
 
*Deadlands has rules for "el cheapo" gear; characters with the Miserly flaw have to buy only 'el cheapo' things. Small items/clothes tend to be only socially awkward, while skill-critical items (saddles) get a 'malfunction number' which is rolled on d20, adding an extra die roll on top of the normal die pool.

*some games reset character wealth between adventures (Barbarians of Lemuria ? ) – emulation of the genre where Conan wins a small fortune then spends it on wenching and debauchery before the next adventure. BoL eschews an equipment costs system in favour of encouraging the GM to let players have whatever equipment they want. "What use is a palace in Patanga, when you are lost in the Jungles of Chush armed with only a sword in your tired fist?"
 
 
*In powers-based systems, resources rating could potentially be modified using power advantages/disadvantage rules, to give an interesting range of effects (characters who must pass a skill check each month to earn their income, who have a variable income month-to-month, are paid in random items by the black market, and so on.
 
 
*D&D 3.x treats cash as a “stock” rather than a “flow” – it is assumed characters will stockpile all their treasure from killing monsters and convert it to magic items, with only small amounts used on consumables. A given number of encounters are required to gain a level, and approximate cash value is known for each encounter, making it possible to estimate the expected wealth of a character of a given level. The model does not however take into account the likely sales of randomly-found treasures to get other more suitable treasure; this would result in replacement characters having up to double the number of items of characters actually played from 1st level, if anyone particularly followed the wealth-by-level guidelines. Additionally, NPCs are much poorer than PCs (their treasure is fudged up to 3x that of a normal single encounter of their level).
Others here have pointed out that the quadratic costing of items (i.e. cost proportional to bonus squared) in 3.5 has fundamental problems because of the curve - going from +1 to +2 quadruples cost, while going from +4 to +5 is a cost increase of only 56%. This curve doesn't discourage either selling off extra items to purchase improvements, or loading up on +1 items (the 'Christmas Tree effect').
 
3E or Pathfinder have items limited to particular 'slots' (e.g. one amulet, one hat, two rings, etc.); 5E D&D instead has 'attunement' which limits a character to having 3 attuned items, which also prevents characters trading items between each other (e.g. hats of disguise). 3E number of slots is potentially modifyable with feats (an epic feat or a monstrous feat for creatures with extra heads, arms or whatever), or dodged around with items built to be 'slotless', have multiple functions or occupy weird slots.

*Some games have certain equipment limited by merits/flaws or archetypes. This sort of idea can work in a short-lived/ 1-shot game, but in longer games causes problems because other characters may gain these items without point expenditure. The Ars Magica character with the merit “superior equipment of faerie iron” may be outdated by another character finding this, or they may just die accidentally and their items end up owned by another PC. In some SF games, complications arise due to even super powers (Synnibarr) or skills (e.g. Cyberpunk skill chips) being purchaseable with cash.
Similar problems also occur with characters whose main ability is being rich (e.g. the slug-like Quan Nobles in Talislanta).
 
Characters sometimes purchase wealth/equipment with “background” points (Storyteller) which may be used for various things such as Resources, Mentors, Allies and equipment; this sort of system is relatively fair since any of these backgrounds are equally mutable and could be gained or lost through roleplaying, rather than using the same pool of “character points” as other character abilities.
 
*some games may have very strange economies where currency is limitedly applicable. A Stone Age game might just use the barter system, if there’s anything worth buying – an assuming characters don’t just take what they want; the “Sufficiently Advanced” RPG assumes a post-scarcity society where information is the only currency. The Slaine d20 supplement (IIRC) uses a traditional Celtic economy which establishes prices in terms of female slaves and cows.
 
*a few games or supplements may have gone beyond basic equipment and into trying to design a detailed economy e.g. Board Enterprises’ supplements on their worlds’ currency (Coins of Fletnern, a free supplement at drivethrurpg – very detailed) and economy (Grain into Gold, which I haven’t read).

Couple of things not mentioned that might deserve a comment

i) James Bond uses a skill system where the score is out of 30 and there is a dificulty modifier to get a target numbr which you roll against on %d. The roll them yeilds a quality number from 1-4 (based roughly on quartiles but actually read from a universal table). The quality rating then determines the level of success ammount of damage etc. as well as generating hero points.
You should also mention the James Bond chase system in vehicals someplace and the method of getting special equipment by spending XP on it.

ii) The Old FGU system games (Daredevil, Aftermath et al) have attributes and talents. Talents are stuff like Combative, Esthetic, Mechanical etc. Talents are generated with a dice roll agaisnt a table to yield a score from -4 to +4 (if memory serves) and then you get a pool to add to them. They are separate from your attributes which are the usual Str, Dex, Int. Talents can get you special advantages and add to your skills so Skills are made up of talent + Attribute + skill points. I only mention it becuase FGU stuff was reasonably influential back in the day and didn't get a mention I could see in your notes so far.

iii) Bunnies and Burrows deserves a mention as well. It had a unique stat system (so you could compare rabbits with , dogs, horses and men) with a 2 number system with the fisrt number giving you a category and the second number a score. It was another FGU game and considering it was published just after D&D in the late 70s it was very advanced being the first game to have a skill system, martial arts rules and putting emphasis on Role play and cunning over kill everything and take their stuff.

Much obliged Jibba-Jibba - I'm not as familiar with some of these but do have James Bond here, and I think have enough detail in your comments to add notes on the others.  Thank you, will fix tomorrow.

Just a quick clarification on StarCluster (3+) - your company supplies equipment it thinks you need to do your job, but it may not supply the best equipment or the kind you prefer. You can get other equipment via a personal wealth system. This maintains a certain base of standard equipment, so even very poor characters have what is necessary.

I don't think it's necessary to change your description, I just wanted to point that out to those who didn't know.

-clash

Hi Clash...yep looking back I can see it could be misread...thanks!

(Also, sorry, this probably belongs earlier in the thread but oh well).
 
The range of attribute scores depends mainly on the core mechanic of the system. Attribute scores are normally designed with the player characters in mind – scores are largely used to differentiate between the PCs and equivalent foes, so typically operate at a human scale.
It is possible that a game will include a wider variety of opponents – much stronger or weaker than the PCs – or that a game may be written as a “Physics engine”, in which case the game is designed to accommodate not just human battles but other cases. Depending on gaming style, this sort of thing may rarely come up and be determined by GM fiat or similar when it does (flip a coin or assign a percentage to determine which rooster wins in the cock fight, or which god wins in the God War), but edge cases may appear where something is critical, or a game setting will make such comparisons necessary.
Occasionally systems don’t quite manage to deal with all the things they probably should: Cadillacs & Dinosaurs for instance has a 1-10 STR scale for humans (inherited from military game Twilight:2000) but doesn’t assign Str to any of the larger dinosaurs, since humans can’t grapple tyrannosaurs. As a consequence, dinosaur-vs-dinosaur (or dinosaur-vs-vehicle) grappling isn’t covered by the rules; this sort of thing is wholly up to GM fiat.
Games that do give everything stats, may not always work quite as hoped. Dice Pool systems in particular scale badly since the pools become unwieldy, hit point vs. damage may not always work at the lower end of the scale (D&D housecat vs. wizard), or Strength modifier may be out of whack with lifting capacity, giving tiny creatures a suspiciously high chance to perform some feat of strength.
 
The range of a normal ability score needs to consider both reasonable dice roll modifiers as well as other game effects based off attributes. For instance if a system limits weapon use by STR, then STR needs to normally fall in a range where a normal human can't dual wield greatswords easily, or extra rules are required to limit this.
Ability damage or reductions are another factor to consider: The Mutant Epoch for instance has a system where attributes average about a 25 but can go up to 100 or so for starting characters. Individual mutations have an APP (Appearance) penalty, but a character with an upside-down face (-4d6 APP) can still be three times as pretty as an average human if they have a good initial APP roll.

Approaches to having a system work at different scales include:
 
*Attribute categories: Bunnies and Burrows (the Watership Down RPG which has PC rabbits) has stats with not just a number but also a category for different creatures (e.g. rabbits, horses and humans all belong to different categories for Str). FUDGE (written by the author of the GURPS adaptation of Bunnies & Burrows) includes a concept of “Scale” which is similar; this has multiple categories, and allows comparison of numbers across different categories.
 
In similar approaches, Savage Worlds gives animals intelligence ('Smarts') rated the same as humans i.e. d4 to d10 or more, with the note that this is [Animal] intelligence; this both prevents animals dropping below the d4 minimum that works in the system, and makes animals reasonably good at resisting Smarts 'tricks' in combat; it requires some interpretation by the GM as to what the limitations of animal intelligence are, but avoids complex patchfixing like 3Es bluff penalties vs. animals, and lets Notice be Smarts based without animals becoming incompetent at perception checks.
 
*Ranks: sort of relatedly, a system can use numbers for normal scores and descriptive ranks outside this. Amber uses a numerical scale for Amberites, who are superhuman, but rank descriptions for weaker characters (who may be “Chaos Rank” or the pitiful “Human Rank”). A similar idea might be applied in reverse for huge attributes, e.g. dinosaurs could have various ranks of Super-Strength instead of a numerical score like humans.
 
*Moderating scores (e.g. using divisors): JAGS and Forgotten Futures are two examples; both use roll-under, but in an opposing contest if both values are very high, they are divided to get a value with a chance of failure. JAGS uses a table for determining the divisor (i.e. if both are 21+, divide by 2) ; there are significant shifts whenever the divisor changes; Forgotten Futures is arbitrary (the GM sets whatever divisor he feels is appropriate to reduce both scores back to 12 or less (2d6 roll under system).
GURPS has "contests of ST for Very Weak/Strong creatures" rules; if both targets have Str <6 or >20, the weaker value is set to 10 and the higher value is scaled proportionally (x 10/lower ST) e.g. a contest between Str 50 and Str 60 is resolved as 10 vs. 12. This is fairly good, though again note breakpoints.
 
*Open-ended attribute scale: A core mechanic may be designed expressly so that most things fit on the single attribute scale; a game can use an additive system where scores have an ever-increasing (logarithmic) value, a table for comparing massive linear values that has built in diminishing returns (Marvel Super Heroes), a ‘floating die’ system or a multiplicative system (e.g. see post #25 in this thread).
 
*Miscellenous special abilities may be used represent a being that goes beyond the normal scale. Dragon Warriors has creatures that get +3 bonuses to damage from Strength (such as golems), even though a 19+ score is normally maxed out at +2 bonus to damage; AD&D has a ceiling of 25 Strength but notes some deities and the like have extraordinary lifting capacity and etc. beyond the usual limits (in Deities and Demigods, Atlas and Magni have strength of 25 [special] and can lift anything; Thor has a strength of 25 [special] and gets a damage modifier of +16 from Strength instead of the usual +14).

Mayor: Er, Master Betty, what is the Evil Councils' plan?
Master Betty: Nyah. Haha. It is EVIL, it is so EVIL. It is a bad, bad plan, which will hurt many... people... who are good. I think its great that its so bad.
-Kung Pow; Enter The Fist[/I]
 
Many game systems may some attempt to control (or at least describe) the moral behaviour of PCs.
These may be just good or evil – either a description or a number which quantifies this more precisely – or characters may have more complex restrictions/motivations. Games may also have specific alignment rewards/punishments hard-coded into the rules (e.g. Marvel Super Heroes).
 
 
Categorical Alignments
The traditional alignment system as seen in D&D gives a method categorizing characters depending on whether they're the good guys or the bad guys. The alignments give a loose description of NPC behaviour, and limit PC behaviour by threatening them with an experience point penalty if they do not conform ("You can't do that, you're lawful good"). In some respects this can be seen as preventing characters from behaving inconsistently, but in other circumstances, this may be punishing characters for actual character development. Alignment is also subject to alot of interpretation as to what constitutes "good" vs. "evil" and when characters crossed the line, as well as generating simplistic conflicts (the paladin is forced to choose between Law and Good). Interpreted overly rigidly, it can create characters that are caricatures of their alignment (e.g. evil creatures with no human relationships or feelings).
Different versions of D&D have had a nine-alignment system (an "ethical" axis of Lawful/Chaotic and a "moral" axis of Good/Evil), a three-alignment system (Lawful, Neutral, Chaotic), or a five alignment system (4E D&D; Lawful, Good, Unaligned, Evil, Chaotic Evil); Warhammer also has similar alignments.
 
Variant rules within D&D included:
*the Dragonlance system - 1st ed. Dragonlance for D&D used a detailed alignment tracking system which had 10 "steps" between alignments, with moving to the midpoints causing confusion and hence penalties (I sort of adopted this in a 3E campaign and gave characters "evil points" for awhile for tracking purposes, until I realized it just encouraged them).
*Severe Desperation- Dark Sun is often seen as being the least compatible with the original alignments, and contained the "Severe Desperation" optional rule where a character at risk of death had to pass a check or become Chaotic Evil with respect to saving themselves (Some aspects of Dark Sun, such as Preservers being able to defile occasionally with the risk of becoming corrupted and becoming Defilers, could definitely have used some sort of number for tracking their progress toward the dark side)
*Planescape retained "alignment", but most planar characters had an outlook probably more heavily coloured by their Faction, which had particular philosophical beliefs and powers. Factions included the Fated, who believed in individual destiny and could never accept or give help to others, the Doomguard who saw it as their role to further entrophy, the Harmonium who believed in spreading law throughout the planes, the Athar working to undermine the deities, and the Free League who refused to believe they were a faction.
Older D&Ds (Basic, AD&D) included rules for "alignment languages", which all characters of an alignment could speak; this probably gave rise to some specific languages like Celestial and Infernal in 3E and later.

Closely related to D&D, Palladium uses an alignment variant which removes neutrals and defines exactly how characters behave (i.e. will/wont betray a friend, kill, steal, or attack an unarmed foe); which at least cuts down on arguments over whether paladins killing baby orcs is good or not. The Palladium alignments included Principled (LG), Scrupulous (CG), Unprincipled (N ?), Anarchist (CN), Miscreant (NE), Aberrant (LE), and Diabolic (CE). Mystic China also includes a "Taoist" alignment.
 
A couple of other games also included descriptive alignment systems e.g. DC Heroes defined a list of "Motivations" for characters which described a sort of personality seed for a character and how they would act in most circumstances. These included Upholding the Good (Superman), Seeking Justice (Batman), Responsibility of Power (Green Lantern), Unwanted Power (Cyborg), Thrill of Adventure (Changeling) , and for bad guys Mercenary, Nihilist, Power Lust, Psychopath (the Joker), and Thrill Seeker.
Omnifray has a "spiritual status" system that describes souls as being either Primordial (pagan), Redeemed (belonging to the angels), Excommunicated (cast out from redeemed status), Fallen (spirit belongs to lower powers) and Unbidden (mystical).
 
 
Numerical (Quantitative) Alignment ("Idiom")
As well as the description-based alignment systems, a number of games use use numbers to define how good/evil characters are: In Kirk's analysis of RPG design work linked earlier, these are described as the "Idiom" pattern. This gives a number that's rollable against for some sort of check, and can be adjusted up/down more easily for PC behaviour. These systems may be less descriptive of NPC behaviour.
 
*West End Games' Star Wars gives characters "Dark Side Points" for committing evil acts. Force-sensitive characters are more susceptible to the Dark Side and so walk a much finer line as regards gaining dark side points. A roll less than current Dark Side points on d6 results in the character becoming (at least temporarily) an NPC. SAGA reportedly has a rule where dark side points automatically add to Use the Force checks.
 
*HarnMaster rolls a "Morality" score which determines a character's behavioural code, and which deities they may worship.
 
*Vampire gives characters a "Humanity" score, which is eroded by inhuman acts unless the character can pass a Conscience roll. The lower the score, the more horrific the acts that could force a check for humanity loss. Later supplements added the idea of "Paths" which characters could switch to instead of Humanity, giving those vampires a different set of limitations.
 
*Indie games may have personality traits which go beyond just regulating character behaviour (as with Vampire) to provide extensive bonuses/penalties to a character on non-alignment-related checks – a not-so-subtle incentive to the player to behave in line with game expectations. Humanity in Sorceror for example determining if a character can bind demons (if low) or dismiss demons (if high).
 
 
Inescapable Alignment
By this I mean that a particular set of morals is actually hard-coded into the game - all PCs behave or suffer penalties, almost as if everyone has to play e.g. Lawful Good.
For instance, Marvel Super Heroes mandates a specific code of conduct for all heroes, in accordance with Silver Age comic book codes; characters suffered loss of "Karma points" for behaving unheroically e.g. killing people rather than subduing them. Villains had a different code of conduct which gave them karma for upholding genre conventions e.g. leaving PCs in death traps with one inept guard. This in effect gave a two-alignment system, though players were always "Good guys"; rough types such as Wolverine or the Punisher just had to live with less points than other characters.[/FONT]
 
 
More Complex Systems & Other Elaborations
*GURPS and the like may handle alignment-related issues via Merits and Flaws which control character behaviour to an extent (e.g. Heroes may get extra points for Compulsive Honesty or Self-Sacrifice). These are more complex than a simple Good/Evil switch; they tend to limit character development greatly (it requires lots of points to remove the flaw) but at least attempt to reward characters proportionally with their role-playing handicaps, and give more potential to customize a character's behavioural limitations to their culture.
 
*Central Casting (a series of generic supplements for any RPG for determining character background) determined a character's "Alignment" with respect to good/evil by rolling their personality traits and determining how many Lightside traits were present vs. Darkside traits. A character's background was rolled on the tables with some events giving lightside, darkside, or random traits.
 
* Dragon #173 had a fairly weird Priority system for D&D which had characters defining an order of importance between aspects such as Deity, Sovereign, Homeland, Comrades (the adventuring party), Race, Family, and Self. Lawfuls ranked all of these, while Neutrals ranked only three or four of these and Chaotics consider them all equally important (or unimportant). Evil characters ranked Self at the top of their hierarchy. In this system characters also had to choose behaviour linked to their traits (e.g. the dwarf honours Family by feasting with his clan when in town); Chaotics received odd superstitions to balance their relative freedom.
 
*Pendragon uses numbers to define personality traits, but with 13 or so different traits rather than a single good/evil axis.
 
*Dying Earth has a sort of anti-alignment system in which characters are vulnerable (unless they buy Resistances) to various temptations such as arrogance, greed, food, sex, laziness, and nitpicking , designed to create amoral characters which make shmucks of themselves as in the original Dying Earth books.
 
*Runequest Cults have come up in discussion of alignment before; RQ e.g. Cults of Prax includes lengthy descriptions of given cultures/religion including beliefs, likes/dislikes, and behaviour restrictions for various levels of involvement in the cult. Touched on here:
http://www.therpgsite.com/showthread.php?t=19345

*DungeonWorld has "alignments" which are a single behavioural trait that earns XP, named 'Good', or 'Neutral' or 'Chaotic', etc. - what the trait demands varies by character class. Arguably these could be considered to be mostly just personality traits rather than a true alignment system, though the general descriptions also prompt assumptions on how characters should behave.

The following is a bit out of order again, sorry...
D&D and simple class-based classes may just have binary weapon proficiencies - different classes being proficient with, or allowed to choose, different weapons. (Very rarely in 2E a weapon might cost multiple 'slots' to learn, e.g. the assassin kit could learn a non-thief weapon for 2 slots, or Masque of the Red Death (1890s-themed) characters could learn 'rare' medieval weapons for 2 slots).
AD&D also had a 'weapon specialization' which cost multiple 'slots'. 2E, not having a 'feat' or special power system, sometimes gave specific weapons unusual benefits for specialization e.g. special Dark Sun weapons in Dragon #185.

Skill-based games: these may have a single "Melee" or "Fighting" type skill for all melee weapons, or different skills for multiple weapons (Doing the latter removes the ability of the high-level D&D fighter to just pick up a lead pipe and beat anyone to death with it, though).

HarnMaster "opens" new weapon skills at a higher default (multiple of the skill base) for experienced characters, but this is still a fairly limited benefit. LegendQuest as noted earlier in skills, has variable-breadth skills which let a character buy either general "melee" skill levels, or specific weapon skills.
Even games with a single "Melee" type skill may allow "skill specializations" or the like with specific weapons; these may be a specific form of skill or purchaseable as an advantage/disadvantage.
Recon has separate skills for primary and off-hand weapon use, for each weapon, while other games sometimes make 'ambidexterity' a weapon proficiency e.g. 2nd Ed. D&D.
FantasyCraft has weapon tricks for various weapons, as well as short feat trees: some feats let characters apply weapon tricks for other weapons, like performing club tricks with your flail, hammer tricks with greatsword, polearm and staff tricks with spear, etc.
 
Weapon proficiencies & magical weapons
Fantasy RPGs usually have magical weapons which appear, which might be randomly generated or placed as fits the GMs conception of their world. Weapon proficiency systems are one factor to consider when determining how available magic items are; if the two aren't compatible you may get either of the following
a) a magical sword etc. goes to the character (/party), but is considered by them to be trash because they can't use it.
b) a magical sword etc. goes to a character which is a benefit to them, but which prevents a character using a number of their abilities (feats, etc).
 
Ability to create magical weapons can prevent proficiency/weapon mismatches. However ability to e.g. produce a +3 bastard sword from nowhere is of limited use if one was going to appear in game anyway.
 
Skill based games with multiple combat skills may have a "use it and it improves" diminishing returns improvement system (e.g. Runequest); therefore unlike some level-based or point-based games characters aren't permanently behind in the long term if they change weapons due to a new item dropping.
 
Feats: D&D 3.x's "feat" system means optimal use of a weapon may requires not just proficiency but also one or more feats; any ranged attacks require Point blank Shot/Precise Shot, reach weapons improve in usefulness with Combat Reflexes, greatswords require Power Attack, quarterstaffs or the various "double" weapons require Two Weapon Fighting, multiple thrown attacks requires Quick Draw, and so on. A warriors' feat choices lock him in to one or a few weapons even though they are theoretically proficient in all martial weapons, even without a character having taken wholly weapon-specific feats such as Weapon Focus, Weapon Specialization, or Improved Critical.
A character has set resources based on their level, so a character who changes weapons (i.e. who takes Weapon Focus: longword, then gets a magic scimitar thats better) is permanently behind an appropriately equipped/constructed character. Consequently, the system is designed to allow PCs to dump awesome magic trash at the item mart for conversion into something useful.
Compare this with say 2nd edition (where a character could pick up a new weapon proficiency every 3 levels or so and so learn to use new items), or SenZar (where characters but can learn a new weapon in just days of training, with no xp cost/feat cost). However even a complex feat system could support characters who know multiple weapons; this just requires characters get enough feats to allow a range of weapons, feats designed to work with various weapons, and splat bloat to not continually expand lists of add-on abilities for particular weapons that encourage specialized builds.
 
Weapon proficiency may be modified by race e.g. races getting particular weapon proficiencies/free ranks in weapon skills for free.
Star Wars' Saga edition is interesting in that many races hail from primitive worlds (e.g. Gamorreans or Ewoks); primitive races generally didn't receive weapon proficiencies in e.g. blasters normally given by class, as a racial disadvantage. This generated a slight perverse incentive for such creatures to be Jedi, since Jedi in any case come with no blaster proficiency (so not suffering any handicap). This sort of ability wouldn't need to be a codified racial feature at all in a skill-based system, where the GM could limit skill selection based on background and potentially have 'civilized' ewoks if that made sense for a given background.

 
Calculating weapon proficiency bonuses:
*In some systems, different weapons may have different skills. Skills may also have varying breadth e.g. LegendQuest, so that a character might have some general "melee" levels (more expensive) and some weapon-specific skill levels.
 
*in some systems different weapons may have differing controlling attributes - particularly in systems with lots of attributes (ROAR used different averages of about 3 attributes per weapon). This can be used to implement different racial weapon preferences as an emergent property (as races have different attribute raises). Done clumsily this can cause oddities; consider how in 4E D&D, player's handbook dwarves gain bonuses to Con which improves their warhammer abilities (via fighter powers) and potentially crossbow skills [Steady Shot]; however half-elves likewise have Con modifiers... and so are good with warhammers and crossbows.
3E D&D defaults melee weapons to Str, with 'light' and some other weapons being able to instead use Dex to hit if a character takes the "Weapon Finesse" feat; 5E D&D separates 'light' from 'finesse' so some light (offhand) weapons can't be finessed and also lets finesse add Dex to damage (possible foobah: hand crossbows are described as 'light' but TWF, the only thing that keys off the 'light' property, only work with melee or thrown weapons). Thrown weapons can use Str to hit. 4E D&D applies different modifiers to both hit and damage depending on power used (e.g. paladins generally do +Cha mod when hitting things with weapons, and need to take a 'Divine Might' power if they want to occasionally deal +Str mod to damage). Marvel super heroes used Fighting to hit, Str for grappling, and Endurance (the basis for movement) for charging, as well as sometimes using separately rolled power ratings in place of stats. HarnMaster (d%) modifies ranged attacks for PER as well as double-DEX.
 
*Level based games usually have a level-based attack, plus either proficiency bonus or non-proficiency penalty; older D&D versions (3E and before) applied a penalty for non-proficiency, while 4E applies a bonus to hit for being proficient (+2 or +3). Older D&Ds gave a variable penalty (-2 to warriors, up to -5 for wizards; half if a related weapon was known) while 3E gave a flat -4 penalty (though warriors were proficient by default in all weapons). Kyle Aaron has pointed out that players are more likely to "forget" penalties, but the penalty does remove an extra addition step from attack rolls; also bonuses also don't change between different weapons, and PCs will generally only rarely use non-proficient weapons anyway.
4Es defense system does simplify (and balance) 'touch attacks' compared to 3Es system, but not particularly better than most alternative armour methods (i.e. armour as damage reduction, or a separate bypass roll). As implemented it results in martial powers - which add weapon proficiency bonus - having quite high chance to hit against non-armour defense.
 
Other elaborations:
*Palladium's Ninjas & Superspies lets some characters learn multiple Martial Art Forms, each of which has their own separate base # of attacks, bonuses and allowed manuevers - flavourful ("My Snake Style will overpower your Crane Style!"), but requiring separate sets of combat info for each Form known.

Strength Minimums
*a little off topic (but this doesn't really deserve a full topic of its own) some systems have Strength minimums for different weapons -
Tunnels & Trolls, GURPS, and Savage Worlds are examples (and T&T also has DEX requirements). Savage Worlds lets characters use weapons with damage dice larger than their Strength die, but with damage capped. Tunnels & Trolls (which has 2-minute combat rounds) assigns minimum requirements ad hoc, and gives characters damage to their Strength equal to the differential between current ST and ST-required of the weapon, so characters using weapons that are too large tire faster and faster, eventually taking excess damage to CON.
T&T Deluxe replaces this with a Saving Roll to avoid dropping a weapon outright on Str or Dex (L1 for 1 pt short, L2 for 2 pts, L4 for 3 pts, L8 for 4 pts, an insane L16 for 5 points - the design problem here being that the save is on the deficient attribute so by rolling the same stat and increasing the level, is essentially 'double dipping' a penalty and guaranteeing its impossible e.g. a character with Str 10 using a Str 15 weapon has to make a Level-16 Str roll, i.e. has to roll 85 on 2 six-sided dice (doubles roll up). About the only thing that could modify the base would be a talent (skill), created with GM approval.
D&D 3E imposes Str minimums for purchasing some particular weapon proficiencies (i.e Bastard Sword and Dwarven Waraxe) although characters can use these two-handed as 'martial' weapons. It also has 'composite longbows' which have varying minimum Strength, although the modifier varies only how much of a character's normal Str-modifier applies to damage; 4E dropped this when it adjusted bows to add DEX mod rather than STR mod to damage (despite bows with different 'pulls' being a thing in reality). T&T actually rates bows of different 'pulls' as different weapon types - Extra-heavy, Heavy, Medium, Light and Very Light bows are different weapons with different base damage dice, DEX required and range; arguably T&T wizards should be able to use 'very light' bows (as 2d weapons)- though nothing larger. It also allows bows to be 'built' or 'backed' [composite] for extra range/damage adds, at extra cost.
Potentially bows with different 'pull' could have different rates of fire, as well.
 
Strength minimums can be annoying in that they limit character's available weapon proficiencies; if a character can increase their STR via levelling up or magic, they also end up changing optimum weapons, possibly making previous weapon proficiencies or magical items redundant. (T&T does this deliberately - some weapons are deliberately out of reach of lower-level characters due to their STR or DEX being too low, or excessive GP cost - but at least as there are no weapon skills, points can't be wasted). T&T also has the issue of characters being 'double hosed' by poor ST and/or DEX, with low scores both limiting characters to poor weapons and also giving additional penalties; the Beta playtest of the Deluxe edition of T&T removed attack penalties for low scores for that reason. The overall design where some weapons are clearly 'better' than others, is a fairly different paradigm to D&D where for the most part it aims for a 'level playing field' where you can pick any 'martial' weapon and have it be equivalent to any other. However T&Ts approach is perhaps inevitable, given its simple combat system where everyone on one side rolls their dice and adds them together, losing side taking the difference as damage. The 4d+1 weapon is distinctly better than the 4d weapon, without it being possible for hit penalties, speed factors, or other variations, so its Str- and Dex- required system that creates winning and losing weapons but limits access to the winning weapons, is maybe the only alternative to just having all weapons be exactly the same.
 
Related to this:
*Lord Vreeg's Celtricia game has separate STR/DEX requirements depending on whether a weapon is one-handed or two-handed.
 
*A Strength minimum system might replace 1-handed or 2-handed weapon rules, or awkward weapon sizing rules: a character can use whatever weapons their total Strength permits, though this requires Strength follow an appropriate range (i.e. haflings actually have to be substantially weaker than humans, and it has to be difficult to reach a Str such that using a greatsword in each hand is possible!). Damage directly proportional to Strength-required can also balance two-handed weapons vs. two-weapon-fighting i.e. the Strength 15 character might be able to use a Strength required 15 weapon (a greatsword) in two hands for 3d6 damage, or a Str-required 10 longsword (2d6 damage) + a Str-required 5 shortsword (d6 damage). (I first saw something like this proposed as a houserule for Tunnels & Trolls). This might not work well for characters with > 2 arms, however.
Note that T&T normally lets a character use two weapons if they can meet the combined STR/DEX requirement, but some weapons are also explicitly called out as two-handed.

*The Fantasy Trip has larger weapons having higher STR-required, and this replaces a Str damage bonus (there's no benefit for using a smaller weapon). It does however adjust unarmed damage for Str.

*Cadillacs & Dinosaurs has a Str-based recoil system for firearms where a character multiples [recoil factor of weapon x number of bursts fired] and, if this exceeds their Strength, the amount over reduces to-hit target numbers (or total dice rolled for automatic weapons fire - cf. autofire notes in combat moves). So, its interesting in that Str-required isn't exactly set, but instead increases as you opt to take more attacks with a weapon.
-similar to that, Nexus: the Infinite City (precursor to Feng Shui), a 'burst' is treated as giving a bonus to-hit rather than an extra attack, but likewise increases Str-required.
-slightly similar to the basic rule, Amazing Engine's "Bughunters" game has Str-requirements for recoil by dividing weapons into "light, medium or heavy" recoil categories; these effectively just translate to a 30, 45 or 60 Str ["Fitness"]-requirement with an extra step. Penalty to hit is -5% per 10% Fitness under the minimum.
-Shadowrun 5E has a recoil # calculated at [1 + 1/3 Str round up] + any 'recoil compensation' bonuses; bullets fired subtract from that and any remainder is the dice pool penalty. It could be more realistic in some circumstances (troll using handgun vs. mage using same handgun), but if characters are assumed to be using 'size appropriate weapons to start, it gives stronger characters an improper advantage, maybe; larger guns should generate more recoil per bullet and the old 'flat' system with no Str adjustment would model it better.

*some rules I was experimenting with let characters 'Push' their Strength as an action to meet Str minimums for weapons, which would therefore apply a multi-tasking penalty (for making 2 actions, the Push and the attack) to an attack roll made the same round.

Either Strength minimums, class-based weapon proficiencies, or complex sets of weapon effects can all serve to ensure that most of a weapon list is useful (depending on what character is being played). Otherwise just picking the biggest damage weapon ends up the best choice (for instance in Unisystem's Army of Darkness, you'd be crazy to use a gladius [Str x 3] since an axe is [Str x 5] with no other drawbacks, and uses the same skill).


Weapons Design
The following doesn't exactly fit here, but in absence of a better place here's a discussion of weapons keywords.

An example of how multiple, somewhat abstract keywords can be slightly complex:
e.g. in 5E the hand x-bow has the 'light', 'loading' and 'ammunition' keywords; as a ranged weapon the light is irrelevant to most purposes to which that normally applies. The Crossbow Expert lets someone ignore the loading property (so can use as many times as they have attacks; but still requires a free hand to reload (the ammunition property). The net result is that its impossible for a (2-handed) character to dual wield hand crossbows firing as a bonus action, but can fire with 1 hand crossbow twice easily. (a character can't benefit from both TWF and Crossbow Expert as both use up bonus actions).

https://www.reddit.com/r/DnD/comments/376m7u/dualwielding_hand_crossbows_the_final_word/


recent edits: T&T weapons design

 

Quote from: InkyHat(From here) I thought Mutants and Masterminds and other effects based powers systems were awesome.
And then I tried to play M&M.

"I slam the door in his face"
"Roll Environmental Manipulation to close the door, and Stun to see if it stops him."
"I was using my hands... and I don't have either of those..."
"Oh, then spend two Hero points to acquire them for the scene."
-Does So-
"Okay, you succeed, he's surprised that you slammed the door in his face."
"I yell to my friends in the other room that the bad guy just showed up."
"Roll Super-Ventriloquism."
"You're shitting me right?"
"Yeah."

This use of the term 'effect-based' is a term first used by Champions/ Hero System to describe how an underlying system can be re-skinned to provide a variety of effects. Note that 'effect' in this context is entirely different to I normally mean by 'effect' e.g. around page 4, i.e. a term from DC Heroes for the amount of damage or other outcome from an action.

This is the first of a few posts on super powers/character power types; this should end up including psionics, magic (divine or arcane), mutation-based super powers and possibly “Chi” martial abilities.
 
This post deals with generic "super powers" e.g. of the comic book variety, which I'm calling the "mutation" power type. This is the sort of abilities seen in e.g. mutants like the X-men; Gamma World type mutant characters function IMHO similarly.
 
 
Defining Characteristics
A mutant (or superhero), in contrast to other power types (particularly magic) generally has only a few abilities, but these can be very powerful. Depending on system, mutant powers may have a limited number of “power points” or may be unlimited use. Power points can tie into an attribute used by normal people if imagined as being ‘fatigue’ (e.g. Hero System’s Endurance, Villains & Vigilantes Power) or may use some alternative pool of “super power energy” that is zero for non-mutant characters (e.g. Aberrants’ ‘quantum pool’, calculated from their Quantum attribute; Savage Worlds' power points). Characters may sometimes be allowed to burn Hit Points or Con Points for extra power points.
Mutant powers may improve with experience, either with all powers having level-based effects (Palladium), or with individual powers having ratings that can be raised by spending XP - either their own specific ratings or potentially some sort of 'power use' skill. Powers may require some sort of activation roll, or function automatically – usually powers are automatic. Mutant abilities can include super attributes, particularly super-strength.
 
Note that whether a power requires an activation roll to use is a separate issue to whether or not the power is binary (yes/no) - the two approaches go together most easily, but a power can also work automatically and have an effect that's variable, or have a fixed % chance of working despite being binary (Golden Open Gaming for d20 needed an 11+ d20 roll to activate a super feat, for example). An activation roll may make buying more of a power useful despite a fixed-effect.
Note that even if a power theoretically functions without a separate roll, it may sometimes have separate failure chances dictated by its design and other game rules, e.g. a defensive power might need a successful Initiative roll to pull off in time.




In a few games, super powers may be the only power type: this includes mutant heavy games such as Gamma World, or Aberrant where a default super type are "novas", evolved humans.
 
In other games a single super powers system may be used for various other power types beyond mutations, potentially including e.g. gadgetry, psionics, or even magic; systems with this setup include Savage Worlds, Hero, and Mutants & Masterminds. In some cases there may still be distinct limitations/advantages for a power being e.g. psionic or magical in nature (e.g. Savage Worlds’ multiple Arcane, Divine, Weird Science and “Super Power” background edges), while in others this is purely flavour (Mutants & Masterminds), at least barring other characters having powers designed to tag from that (e.g. someone else selecting a disadvantage with a 'not against psionics'-type limitation).
The Invulnerable RPG has various 'origins' which set power source e.g. mutant - biological, battle suit - tech, etc. Characters can split their points between multiple origins and so have multiple power types (creating e.g. Wolverine type characters); additionally it makes 'tech' powers more common since a character can take the 'Implement' power modifier to make another power due to a super-device.
Effect-based games may be quite good for converting characters between systems, since a mechanical framework can be chosen that somewhat matches the original system, whatever it was.
An effect-based approach is somewhat incompatible with a 'class' system for characters (why would you separate powers into two piles -one for each class- when the underlying basis for both sets is identical? How can you make the classes different if they are?) though they may have archetypes.

 
A system may sometimes be designed around one power type mainly, with this 'reskinned' for rare or obscure cases - making a sort of bolt-on effect based approach. For example, mutations in Gamma World 5E (the "d20 system" based version) are generally just for mutants, but there's a "Feral Machine" robot type, which rolls a number of "pseudo-mutations", based on these machines having wearing down of various parts or jury-rigged extra parts.

 
Rating Powers
Methods for determining how strong powers are include:
 
a) Fixed effects depending on character level (Palladium).
 
b) Individually defined power ratings (e.g. Marvel Super Heroes; 2nd and 4th edition (1992) Gamma World). MSH randomly rolls power ratings on the same scale as attribute scores, which is often convenient as a basis for other game functions; Powers range from Feeble (2) to Unearthly (100) and beyond; Savage Worlds’ “Super Power” arcane background edge lets characters buy a power as a skill (which in SW have the same scale as attributes). The 1st ed. of Mutants & Masterminds bought powers as skills as well (level-based ratings) though probably an attribute-based model for powers would be better.
Power ratings sometimes directly determine damage (e.g. in MSH, an Incredible (40) rated power does 40 damage basically regardless of which power it is), while in other systems damage is assigned based on the power, with power rating perhaps adding a bonus e.g. in Gamma World 4E "Hands of Power" might do 3d6+ mutation modifier damage, while "Thorns" deals 2d6+modifier and "Quills" is d6 with no power score. Having power rating directly determine damage does generate a huge incentive to buy one attack up to maximum and spam it continuously.
Probably the best example/argument for power ratings was DC Heroes; its AP system lets the same power set work for both 'street level' and 'cosmic level' games, and exactly defines a powers' range, damage, duration etc. in real-world terms.
Most 'successful' designs using power ratings on this scale use random-roll power rating determination, since point-buy will lead to potential abuse (and unlike attributes, number of powers may vary meaning a purchase system has to give reasonable numbers whether a single power is bought, or several).
Gamma World 4E power ratings also made it possible to add level-advancement to powers e.g. Espers and Enforcers gain +1 per level to mental and physical mutation power scores respectively. Some powers are random but don't have a 'power rating' e.g. multiple arms being just +d4 arms. Potentially, these powers could be instead designed to be power-rating-based (i.e. a power rating of 5 = 1 extra arm, 10 = 2 extra, 15 = 3 extra, etc.) which would give more of a 'curve' to results than d4 and/or be more consistent - but would actually lead to problems with Enforcers growing more arms as they went up in level. Consistent ratings are useful for the purpose of purchasing powers and perhaps other manipulations of the score, like 'damage' to ratings from 'power nullification' type powers, though ad hoc costs without a consistent power score are possible just more complex (HERO).
One workaround for the issue that point-buy powers are incentivizes to spam a higher-rated power continuously is seen in JAGS special abilities book (free from the jagsrpg site); extra attack powers cost 1/3 the cost of the main attack power. Players can also be incentivized to have multiple attack forms if resistances to particular damage types, etc. are reasonably cheap or effective (in the same way multi-classing can be more valuable if a single-class character can end up fighting a monster immune to their main shtick).

Powers bought from a point budget are more likely to have variable costs (e.g. you can spend 10 points to buy a power worth 3 points, a power worth 2 points and a power worth 5 points) whereas this is difficult to do with randomly-rolled powers (compare "roll four mutations" a la Gamma World - no way to implement different costs). Different costing can be done in a very basic way by having separate lists of 'minor' and 'major' powers e.g. Palladium. This also reinforces having power scores for games with random-roll powers - as with skills its typically difficult to have variation for both number of power levels and different costs for each power.


 
c) Power working with an ability check (i.e. 7th Edition Gamma World, a variant of 4E D&D)
 
d) A power may have a skill rating to use, in addition to a rating of its own (e.g. Pathfinder has a Fly spell based off caster level, + a Flying skill for using it).

e) Some powers may be binary – you have the power or you don’t.
(Even in this case, it may be possible for the system to vary how good character's are at powers by adding other powers - 'meta powers' if you like - that apply advantages, let characters spend more PPs, add bonuses with them, or whatever.Its just a question of whether this is frequent enough that it becomes more awkward this way than just having ratings).


Including attribute modifier in a power formula has an unbalancing effect by increasing the importance of that attribute for a character. Generally skills are useable untrained, so that attributes can be important on skill checks whether these are learned or not, but a character who gets several unique CON-based Powers will have their CON become more important, though its cost is unchanged.
(Buying abilities separately, but up to a cap determined by attribute, mitigates this, e.g. Linking in DC Heroes).
 
As an example Aberrant has powers which are rated from 1 to 5, but a normal check is [attribute dice+power dice] - similar to how skills operate in its parent Storyteller system. However, for standard power activation checks attributes and “Mega Attributes” were more important that power rating, though some things (such as damage dice) depended solely on power rating. This caused power rating to be very important for some powers (Energy Blast), and not worth increasing with others, even though both had the same per-point cost. Advantages also increased the cost per point of power rating, so these were more affordable at lower power ratings.
 
Separate power ratings also decrease overall impact of high attributes on the game (good for game balance), reduces racial typecasting (i.e. all of race X are good with power Y).

Superhero games are usually more likely to have different power ratings for characters, whereas post-apocalyptic games have more yes/no abilities - partly because that generally works fine for creepy mutations like crab hands or antennae, partly since PA games are fixed at a lower power level and don't want to simulate planet-shattering potential levels of power.
 
 
Power Determination
 
 
Powers might be determined by random roll or be point-based.
Pros/Cons of random rolling:
 
*faster character generation
*does feels appropriate (IMHO) for Gamma World type games.
*doesn’t allow players to build specific concepts
*possibly unfair. A random system might just randomly determine which powers a character gets (which may be OK if the designer has designed an array of fairly useful powers; possibly separating them into “major” and “minor” lists before rolling), but if a random roll also determines how much of each power (i.e. +d4 extra arms), hopeless or overpowered characters may be possible.
Gamma World has traditionally used a random array of mutant powers; earlier editions gave each character d4 physical + d4 mental, while by 4E PCs only rolled for the 'split' of mutations (0-5 physical based on a d6 roll, with the remaining 5 mutations being mental; more might be gained still via a roll on the table of 'roll twice', or extra d3 mental from a 'dual brain', and a bad roll could give some 'defect' mutations). Earlier ancestor Metamorphosis Alpha lists opposing mutations (e.g. a character can't have both 'wings' and 'total carapace'). Gamma World's power list is sometimes quirky since some mutations are more for the monsters - e.g. "symbiotic attachment" is more designed for a "Puppet Master" type monster that attaches to a PC (control via physical control, though it could be slightly useful for a beast riding character).
The more recent Mutant Epoch RPG has another very impressive list of specific (non-effect-based) random mutations; its notable for including with appearance penalties for each disfiguring mutation; RPG deadEarth had a huge list of "radiation manipulations", with the possibility of getting more in play; it also had a number of interesting 'meta' mutations (removing or altering other mutations) but also oddly included a number of personality disorders, religious observances and other things on the tables. ("The danger on deadEarth isn't that the Giant Radiation Ants will eat you. It's that they'll call to your house with pamphlets. Or iron and fold your clothing. -Balbinus). PCs could also roll fatal mutations in character generation (if not their last mutation a character could keep rolling to see if another mutation cancelled the effect). Number of radiations rolled increases with age (as does skills), though stats decrease. Mutations formed a 'list' with some mutations have position-dependent effects e.g. affecting the prior rolled mutation or mutations 'above' them in the list only. See rpg.net thread  http://forum.rpg.net/showthread.php?473443-Necro-deadEarth-why-isn-t-this-game-on-anyone-s-quot-Worst-Games-List-quot.
Another mutant RPG, Mutazoids, has characters roll for various features like head shape, eyes, etc. separately for each.
An interesting twist on random mutations might be to have each mutation randomly roll body location (one 'spikes' mutation that could have different effects in different spots). Defect side effects could happen if it replaces what's normally at that location (the way a mutant gene replaces a normal version of a gene), and/or there could be a roll to see if it just is extra ability, and perhaps a character might be allowed a number of re-rolls or shifts around which might have to be used if someone rolls something lethal, like both lungs being replaced by something except gills.

7th Ed. Gamma World (the D&D-4 compatible GW), gives characters mutations that change continually, based on power cards, due to reality flux (7E GW is partially radioactive but is due to a collision of a huge number of parallel worlds, not just nuclear war). While still random a character's power suite is only stable inasmuch as its based off the player's deck.



Point based or selectable lists of powers - are used to let characters be built to a particular concept. In purchase systems Limitations to powers frequently have a cost per point (Hero, DC Heroes), though this makes accounting more complex. As noted previously under advantages/disadvantages) Hero distinguishes between adjustments applied per point and “adders” (which have a base cost). Systems may also have varying costs for powers depending on how powerful they are. MSH lets characters raise a score one "rank" by choosing a limitation, even though it generates powers randomly; this provides an erratic increase in rating, due to the way rank numbers increase (2/4/6/10/20/30/40/50/75/100), though allowed limitations also change between ranks.
 
Random roll power determination will usually give weird sets of powers which may be fine (the idea being that a Gamma World mutant should be as weird as possible). Superhero games using point buy may desire characters to have 'themes'; Aberrant for example has no specific rules, but, expects the GM to enforce character-building to some sort of motif (it being suggested that's psychologically necessary and only a couple of super-beings like Divis Mal have outgrown that). "Mutant City Blues" for detective game Gumshoe apparently has a 'Quade Diagram' where less-related powers cost more points; this is intended to support the detective idea as multiple very-unrelated powers could suggest multiple perpetrators at a crime scene.


Power Design
 
Evolution in design of power lists has tended toward more flexible, generic powers. A game might have separate mutations for “Radiating Eyes” (bolts of radiation from eyes), “Hands of Power” (bolt of energy from hands) and “mental blast” (telepathic attack), or these could be covered by a single “Energy Blast” type power. More broadly, a single damage power might include a variety of attacks.
 
Broader powers work better where power advantages or limitations can be applied to better adjust exactly what a power does, or where there is a loose rule framework that allows reasonable interpretation (Savage Worlds would let you get away with saying your Bolt is “fire” and having reasonable effects; in HERO you may need to define detailed advantages/disadvantages for “continuing to burn” or “doesn’t work underwater” if you want those things).
Another thing to consider with broader, more flexible powers is that rolling several abilities into one can complexify rules text (if it needs to note caveats that previously applied across several powers). Consolidation of powers that have similar mechanics into one can be risky if the abilities should be costed differently e.g. (from one of my games) Extra Legs and Extra Arms might both give an extra reroll or action, working similarly, but the ability to make an extra attack is probably much more valuable than an extra movement roll, so they may be better off as different powers.
 
Unusual uses of Powers
PCs occasionally attempt to use powers in unusual ways or beyond their nominal limits.
 
Hero has a power use skill which can be rolled against for unusual situations - Superman crushing coal into diamonds, or frying an opponent you can't hurt with your Jet Boots (which are actually the Flight power). However, using a given trick more than once requires permanent point expenditure to buy whatever power is being copied.
 
Similarly, TriStat dX lets the GM give characters 'attributes' (powers) for free, giving them a cost (from advancement points) if 'circumstances change  and the attribute becomes useful on a regular basis'. Consequently, a player being creative may get charged character points, which they wouldn't if they didn't work out a use for it.

MSH has Power Stunts which can be learned; each attempt to use a stunt you don't have costs a considerable number of Karma points (which are both 'safety valve' points and an advancement currency), and requires a power roll at Red (most difficult) intensity. 3 successful attempts adds a Stunt to the characters' capabilities permanently, for free use thereafter. This is one of the only instances where using advancement currency to boost die rolls works well, IMHO; in any case I find this slightly more logical than the Hero approach, and it gives away no freebies.
Defined Marvel Super Heroes characters sometimes come with some 'power stunts' they use from the comics, as well as some variations in their individual power description from the default listed.
 
DC Heroes doesn't have unusual situation power use rules, but does allow expenditure of Hero Points to temporarily increase ratings to increase areas/durations/etc ('Pushing'). Potentially a character could buy a low rating in a new power on the spot (with GM permission) and immediately Push it for greater effect, but the point costs involved would be quite high.
 
Aberrant allows temporary duplication of some advantages on powers with a Quantum roll ('maxing' a power). This costs power points and botching a roll results in a character gaining Taint, a somewhat bad thing since this permanent gain gives a character physical and mental aberrations.

Unusual elaborations on powers system
The Mutant Crawl Classics (MCC) variant of Dungeon Crawl Classics has mutations which appear similar to its spell 'klutz' system, with use of a mutation requiring a roll that can give a defect or alter the landscape, etc.  Passive mutations (like # arms) can be re-rolled when a level is gained (rolls get +level so a reroll will eventually be worthwhile; Luck or taking ability damage for eating radioactive stuff also give bonuses). Defects also have their own tables, with a '1' giving a reroll (potentially better than a '2') but usually also a second defect, and a 20+ sometimes being beneficial; re-rolling defects with level advancement may change them excessively i.e. an 'oversized body part' might be a head one level, then hands another level (different penalties).  MCC characters can also gain or lose mutations if they roll a 1 (lose) or 20 (gain) making a Fort save vs. radiation damage; the craziness of MCC is such that a character might roll a 20 and gain a mutation, but then its a defect, then another good roll makes it beneficial.
Appearance is level-based in MCC - a mutant gets a level-based initiative bonus from 'horror' -though specific mutations also have set adjustments e.g. to AI recognition, with defects likely to become less horrific after some level advancement re-rolls.

Note: one interesting comparison between systems is that what may be a "power" in one system may be just a built-in feature of all characters in another system, due to changes in the underlying abstractions of the system or how values are allowed to scale. Examples here include:
3E D&D spell/item healing vs. 4E D&D 'healing surges'
Bonus actions from Haste only, vs. bonus actions from the action system
Armour vs. 'soak'.
Luck as a special super-power vs. built-in rerolls (bennies, Willpower, karma), or even an extra dice on all actions (Savage Worlds' 'wild die')
Reality control or Wish as a power, vs. shared authorial control for players.
'Powers' in this sense could stretch to include things given by magic items too: a 3E D&D character can freely level-up and take a level of a different class, while an AD&D character (who wasn't human) could do that with a "Hat of Difference" (1e Unearthed Arcana/2e Encyclopaedia Magica).

A result of that, for instance, is that converting a written adventure from one system to another may sometimes involve adding extra powers or magical items, to try to maintain a particular outcome or have a character with the same sort of feel. This could also be an approach when trying to convert PCs between systems, but may be seen as less kosher - preserving system 'artefacts' in a different rules set being to give a converted character an unfair advantage over native characters (generated in that system).

Edit notes: note on PA games(*), MCC note (*); 'meta powers' (*); DC Heroes note (*); Invulnerable note (*), most powers-on-attribute-scale systems being random note (*); power activation notes (*), Feral Machine note (*)

Flexibility of powers
Comparing say supers vs. wizards: a super might have only one or a few abilities, while a wizard-type character might have several to dozens of spells. [This difference is forcibly avoided in effects-based games; wizardry might sometimes be explicitly defined as a power to get around problems there, or IIRC Hero has 'power framework' rules and the like].
However, super abilities would tend to be more flexible; they may be equivalent to several 'spells' each in terms of what can be achieved. One thing I found interesting for example (in a game I'm running) is to compare Gamma World 4E telepathy with AD&D psionics; Gamma World has one power called 'telepathy' with a number of functions including scanning and communication; by contrast in 2E AD&D there's a somewhat wizard like 'psionicist' class which has an entire 'discipline' called Telepathy, including contact (to get telepathic powers to work on a target), one-way telepathy that can distract (send thoughts), two-way telepathy (mindlink), defense modes, attack modes, etc. - with definitions of whether language is necessary, exact ranges, etc.
One Gamma World power does a noticeable chunk of what the whole discipline does. Given the choice between which approach to use, the detailed list of specific effects would also let someone pick up a few unrelated powers that could be useful.

Post-apocalyptic mutant games do vary from superhero games in that a superhero is most likely to have a few powers that are similar thematically, while a mutant has a varied assortment of weird powers. Supers games may have 'big' powers with various special abilities, or extra enhancements.

the superpowers section seems a bit "Aberrent heavy" I assume this is becuase it's your go to supers game. However it feels a bit odd becuase its not in most people's top 5 Supers games (I would predict these would be Hero, Champions, M&M, MSH, V&V...), unlike using D&D as a standard for Fantasy games.

Also there is a fundamental design decision in Supers games, does the system work as a physic's engine or is it there to emulate the genre. Generally with Supers more than any other game genre it's the second choice that carries the day.

Lastly do you consider feats in 4e to be super powers? In many ways they play like super powers and in a 4e modern game you could basically include all the same feats and they would feel like super powers. On that basis should you include levels and feat trees as an alternate super power advancement paradigm?

Hi Jibba Jibba, thanks.
  My main supers game these days is MSH (though that's just a few one-offs). I have played more Aberrant than anything else (two campaigns of it) but not since soon after it came out. What I will do is add more references to some of the other discussion, and move the discussion of Aberrant mega-attributes to the Attributes section since it’s a bit off-topic. I should admit I've used Aberrant as the example of why powers getting bonuses off ability scores are bad partly since I've probably flamed 4E enough already
 
  Genre emulation vs. realism I guess is important; I hadn't thought of that but this probably should get discussion in some sort of "considerations for designing different genres" type post, rather than here, which was intended to be about super powers/mutant powers, not supers games generally? Thanks, anyway.
 

  On the feats: Feats in D20 System derivative games can be used to buy some abilities that look like powers, and some abilities that aren't.
 
  I guess powers in 4E (or 7E Gamma World) also are also bit super-ish (Fighter 2 utility "Regeneration" comes to mind); but from what I know I think 4E feats are generally more limited than 3.x feats and usually just give minor damage and save boosts and the like. There may be some by now that let you do stuff like you used to be able to do in 3.x – aasimar shooting Searing Light from their eyes, Fire Resistance, Draconic Wings, etc.
 
  A 'tree' structure (feat chain) isn't often used for super powers since supers tend to start out with most of their powers; its easier to just make more powerful abilities cost more. There are  3.x power-type feats that work like this, but I think this is largely due to powers being shoehorned into the existing structure perhaps originally meant to prevent fighters getting stuff like Manyshot or Whirlwind Attack at 1st level.

  Though come to think of it Vampire Disciplines are sort of super-power ish as well, and also something like feat trees in practice (buying each new dot adds an all-new ability). This has the added advantage over a feat tree that you have a number (the Discipline rating) which can be rolled for checks if needed.  

  With regard to whether feat trees are themselves a good idea, there’s a Frank Trollman piece here that’s of interest (the “Failure of Feats” bit about a third of the way day): this basically points out that in D&D switching feat chains means your high-level character is now getting a 1st-level appropriate feat; his solution to that to remove trap options was the multi-functional scaling Tome feats.
  http://www.tgdmb.com/viewtopic.php?t=33294&postdays=0&postorder=asc&start=2

The following is a quickie basic super powers list, with some general notes.
The same powers list might basically apply to spells, psionics or other power design, as well as mutant powers. These are fairly generic powers; subvariations are listed after the semicolon. Other specific powers may be combinations or flavourings of these. I doubt this is exhaustive, though I’ve looked through a few systems to compile it.
 
 
Aid: assist ally (roll or statistic). May also be represented as another power with a "useable on others" type advantage.
 
Absorption/Armour/Damage resistance- absorb damage or effect. Psychic shield or other 'armour' powers (social armour? resistance to knockback? etc?) may use same system as regular armour. This might also be a subtype of Power Resistance, to the "Damage" power.
 
Afflict e.g. Disorient, Stun, Curse, Devolution, etc. This might apply a defined "condition" like weakened/dazed, or it might give a target a Disadvantage, with these largely replacing conditions.
 
Animal/Plant Control; speak to animals/plants
 
Astral Projection; more likely a magic or psi power.
 
Bestow Power to others (e.g. “grant mutation, psionic "Psychic Surgery"). Needs tight controls on use.
 
Clone - create duplicates of character.
 
Computer Interface
 
Damage: Claws, Disintegrate, Bolt, Mental Blast, Poison, Weapon, Immolation (damage aura), Breath Weapon.
This may break down into a number of more specific powers. Choices like different energy types are likely to require different sorts of resistances. Damage might be allowed to have multiple types (as in Gamma World 7E for energy types) giving increased ability to bypass resistances.
May include damage to non-HP e.g. attributes or mental HPs, or this may be a separate power.
 
Darkness Generation; Fog, "darkness" to alternate sensory types.
 
Density Control; may (or not) be taken as "always on" for very heavy characters.
 
Digging: DC Heroes has this, with very specific rules on volume (RAPS for power use = volume excavated, possibly reduced by material hardness. The effect of 'hardness' could suggest this power could get an 'armour piercing' type power, even though its not exactly 'damage'.

Dimensional Travel
 
Divination: e.g. Psychometry (generally a psi power), Scrying
 
Duality/Schizm: additional mental actions
 
Duo-Dimensionality
 
Elasticity
 
Energy Control: one energy type
 
Enhanced Memory/Total Recall
 
Enhanced Senses: Darkvision, Infravision, UV Vision, Radar, Sonar, Hgt. Smell/Taste, hgt. hearing, Telescopic/Microscopic vision, Directional hearing, hypersensitive touch, x-ray vision. May give vulnerabilities to sensory attacks.
 
Environmental Adaptation; water breathing, vacuum, temperature adaptation
 
Extended Lifespan
 
Extra Body Parts; e.g. Extra Limbs, redundant internal organs; this power may also be represented by taking other powers (e.g. multiple actions or extra HPs) and flavouring it appropriately
Detection: various e.g. Life, particular power category, particular Power, weakness detection
 
Flash: deactivates target senses
 
Flight: Floating Disk; Levitation, gliding (winged may be a disadvantage; body part as power focus).
 
Force Field
 
Healing: Resurrection, Damage Transfer. Regeneration may be form of healing applicable to self, but is more likely to be an ongoing power. Healing usually has firm limits regardless of whether most powers are unlimited use.
 
Independent Body Parts - separate body parts to act independently; Swarm
 
Internal Dimension
 
Illusion Generation
 
Immobilize; Stun Ray, Web, Entangle, etc.
 
Intangibility; Gaseous Form; Permeation (e.g. "Meld into stone")
 
Invisibility
 
Kinetic control: Telekinesis, Gravity Control; Magnetic Control may be TK with limitation "metal only".
 
Light Generation
 
Luck: (adjust dice rolls). May be an attribute in some systems rather than a power.
 
Matter Creation
 
Metempsychosis (Personality Transfer)
 
Mind Control: Hypnosis, Domination, Pheromones, Emotion Control
 
Movement (other): Climbing, Jumping, Water Walking, digging
 
Multiple Lives; may be variant of Healing (Resurrection) with target: self.
 
Negate Super Powers
 
Omni-power: duplicate various powers, usually at additional cost. Selection of multiple powers may be limited i.e. a "power framework". Shapeshift may be a specific example of this.
 
Premonition
 
Power Resistance: e.g. specific power (Poison Immunity, Illusion Immunity (true seeing).
 
Power Reflection: (specific power, powers generally)
 
Power Vampirism/Transferral
This usually is temporary, since permanent power transfer is difficult to balance. The fairly-unbalanced World of Synnibarr has permanent power absorbtion (letting a character take anothers classes, mutations, etc.) but this can be a limited number of times, and if the target is higher level they have to save vs. 'burning up'. There are also intrinsic limits on # mutations, and Guilds for the various classes also mean that unusual powers might be noted and punished as murder.  
Rogue of the X-men in FASERIP can permanently absorb powers as is established in the comics, but loses a Psyche rank if she does so (becoming an unplayable mess of multiple personalities if this falls to zero); stealing powers could also be punished under the games' Karma rules.
The Big Bang Comics RPG sometimes always new powers to be gained, but with a character having to take a Qualification after levelling-up, in order to help balance the power gain.
Vampire lets characters steal 'generation' and dots of things off other characters with 'diablerie', but the character gets only minor increases and it leaves black spots in the aura that can be noticed with the Auspex power, leading to retribution for Camarilla characters, though there is a Merit that conceals this. Mage has a 'Shattered Avatar' merit that lets characters share their avatar/soul with other mages, who might be killed to increase it (or seek to kill them).
 
Regeneration
 
Shapeshift
 
Shield
 
Size Control: (grow, shrink) - may be super-attribute if game has Size score.
 
Skill Boost; super linguistics, Mechanical/Economic/etc. genius
 
Sound Imitation
 
Summon
 
Suspended Animation
 
Sustenance: eat anything, solar sustenance (as plant), reduced needs.
 
Super-Attribute
 
Super-Speed: in games with a SPD attribute, may just be a super-attribute
 
Telepathy/Empathy
 
 
Time Travel/Time Control: will probably destroy your campaign. Oh well.
 
Transform (creatures)
 
Transmutation; change state or condition of matter
 
Travel: Teleport, Warp, Teleport Object, Dream Travel
 
Voodoo (zombies)
 
Weather Manipulation
 
 
 
 
Note: Random roll mutation systems may include "defects" which are included on the mutation tables to be accidentally rolled instead of a beneficial mutation (e.g. Gamma World through to 6E).

Edit Note: Interesting thread here on the worst powers ever: http://forum.rpg.net/showthread.php?501260-Absolute-Worst-Powers-Abilities-Ever

Here I'm discussing the idea of limitations or advantages that modify specific powers.
These can be subsets of a general advantage/disadvantage system used by characters, or this may be a specific subsystem just for powers. (Some of this is applicable to general advantage/disadvantage systems).

Alternatives to Advantage Systems:
Sometimes instead of a separate 'advantage' system, a character might add extra abilities to a power just by selecting a different power (meta-power as it were). (This doesn't let the system duplicate disadvantages, though).
A power might also gain extra special abilities from having a higher rating if characters can purchase variable ratings, or characters may be able to purchase special skills which apply extra effects. Sometimes a power may allow customization options which carry inherent customization drawbacks (e.g. 'electrical, -1 damage per die but ignores AC of metal armour'... or something like that).

Variables in costing limitations
Variables in properly costing a limitation are:
*severity of limitation
*frequency of limitation
*strength of power affected (number of points in it)

Severity is somewhat circumstance-dependent; indeed there may be situations where a disadvantage becomes beneficial. "Energy blast affects only mutants" is helpful when you're trying to hit a mutant who is grappling your girlfriend to carry her off, even though it means that later on, the robots in the wastes won't be affected. "Requires oxygen" in a blast type power might logically be used to suffocate opponents in close confines.

Frequency of a limitation occurring is somewhat campaign-dependent, but designers frequently assume a likelihood and use this to preset different discounts for different disadvantages, based more or less on the first two factors; potentially a GM can adjust costs if they really need to (i.e. "only useable underwater" in an aquatic game).

The third factor (strength of powers) may be inapplicable depending on the system - e.g. if powers have no individual ratings i.e. are just level-based or use ability checks. Its more often not bothered with. Note that if a disadvantage has a proportional benefit, characters with high power ratings are compensated for taking it more fairly. On the other hand, if a disadvantage has a fixed benefit, characters should probably not cripple their strongest power; bad design in such power systems occasionally give away weak powers for free (Golden D20).

Most existing systems consider only some of these, sometimes none of them - a trade-off between complexity and game balance.
From simplest to most complex, more or less:

*all disadvantages worth same number of points. If powers themselves are fixed in cost (i.e. selecting 1 Hindrance gives you 1 Edge/power) then having a negative hindrance that affects two powers is equivalent to buying those two powers at half cost. The disadvantages can themselves be designed to be somewhat equivalent [in severity and frequency].

*To pay for a disadvantage, Marvel Super Heroes (FASERIP), as noted previously bumps up scores to the next highest Rank, an erratic increase which is a good deal if your attribute is 10 (a 100% increase), and probably a bad idea if your score is 30 or 40 (an increase of only 33% or 25%). This is probably the simplest system that gives any sort of proportional benefit from taking a disadvantage; the erratic increases are somewhat excusable in that some limitations can only be taken if your power rating is low. There is no extra benefit for taking a disadvantage that's particularly bad, though (e.g. "power useable only once ever").
MSH has 'power stunts' (extra uses for powers) that basically are advantages.

*advantage/disadvantage cost varies by which is selected, but with no proportional changes in power rating (you get +5 points for having your Laser Blast not work underwater, or +10 if it only works on blue objects). (Ars Magica has a lot of flaws that work this way, though with magic rather than super powers).

*A I was working on uses a relatively quick n' dirty modifier of 1/2 cost for a disadvantage, +1/2 cost for an advantage; cost is unchanged if one of each is selected.

*Aberrant has power 'Extras' that increase their costs (a level 1 power with an Extra becomes a level 2 power for cost purposes), but no limitations. It doesn't have general Merits/Flaws for characters (in the core book, anyway).

*Amber gives powers a point cost, with characters able to buy a 'block' power with various aspects or a 'partial power' that does just some stuff (going on thread info; I believe each power has an individual partial power cost scheme, perhaps similar to how DC Heroes runs skills/subskills).

*GURPS may apply modifiers as percentages e.g. -30% to cost (IIRC).

*Fuzion IIRC has base disadvantage/advantage costs, which are also modified for [Frequency x Severity]. (actually its general disadvantage system).

*DC Heroes applies modifiers to both 'base cost' to buy 0 points of a power (0 points is a defined quantity; not having a power has a null value), and a 'factor cost' (from 1 to 10) to purchase a number of points in it; this requires using a table. Advantages/Disadvantages modify Factor Cost but rarely base value, so Disadvantages don't readily allow characters to buy up large numbers of different powers cheaply. More rarely a character can modify a Power by taking a second Power -   "Self-Link" for instance has a whole power write up, though has a fixed cost of 50 points, or a character with Power Reserve and Energy Absorption can also take an advantage "Energy absorption adds to Power Reserve".

*Hero adds limitations of various values (-1/4, -1/2, -1, etc) to a base value of 1, with a negative number becoming a divisor to the base cost. This lets alot of modifiers be stacked onto a power - potentially abusable but allowing for very detailed customization. Hero modifiers are sufficiently detailed that they require campaign-dependent adjudication (will the PCs be going into Vacuum alot, so that "powers doesn't work in Vacuum" is viable as a limitation? This is considered less scientifically than Fuzion, but the overall process is probably more complex). Hero also has 'adders' with fixed cost, rather than variable cost.

*Invulnerable has especially lengthy lists of 'enhancements' for each power - many powers having 10+ possible enhancements. Enhancements are binary things (you have it or you don't), with characters getting 1-10 'free' enhancements based on their power level (unless traded in for attribute points); this is slightly awkward in that Enhancements can cost more or less - they cost the same as the first level of the power - so characters should pick expensive enhancements for free e.g. for hyper-attributes. Slightly worse than this, the same Enhancement is sometimes available for different Powers at different costs (e.g. Adhesion is the same from Extra Body Parts or Elemental Control, but elemental control is Expensive whereas extra body parts is cheap). Its interesting as a game that gives out lots of enhancements as part of power design (the example Human Torch type character has half a dozen enhancements for their elemental fire power). It has Power Modifiers as well; these can be applied just to enhancements (e.g. fire control has 'flight' as an enhancement, so a super-fast modifier can be applied to that) or the whole power.

Now a question I don't have an answer to: Disadvantage systems may encounter a sort of philosophical problem in design; how much is something a Disadvantage that the players should buy, and how much should be hard-coded into the rules itself? Should constructs be immune to death ray because they have a power that gives them resistance to it (costing them points), or should I logically have to buy a Disadvantage so it doesn't work on them (giving me points)?  Should water have Resistance (fire) or should my fire blast have the disadvantage "doesn't work underwater?"


Also, below is a partial list of Advantages/Disadvantages (one list since many are reversible).

Armour Piercing/Low Penetration   -requires system to be able to adjust armour penetration, or gets messy
Counter [specific attack advantage] i.e. Impervious (ignores armour piercing)    -may be costed as cheaper than equivalent attack advantage; difficult for defenders to optimize all defenses.
Ignore defender resistance i.e. no saving throw, Aggravated damage - generally unbalanced
Secondary Effect e.g. condition applied as well as damage
Quicken/Slow        -if extra attack becomes a "free action" to use.
Additional Roll Required to function (Disadvantage) e.g. skill check (this is a poor balancing mechanism with variable cost disadvantages, since this will have little effect if other score is high; it may work somewhat for fixed-cost disadvantages as can be balanced for a worst-case scenario i.e. maxed out skill). HERO 'requires a skill roll' limitation is also problematic in that it [4E] suggests a character making the skill roll by X can increase the effectiveness/active points by 10%, making the limitation in some ways a bonus.
High Damage/ Low Damage - poorly designed advantage usually; often the main benefit of rating increase is extra damage making this a min/max dodge.
Burning (Continuing Damage)
Area        Clearly an advantage, though if can't be turned off it has its downsides.
Reduced Power Point Cost   / Increased Power Point Cost   - these can be problematic combined with powers that can generate PPs (giving a loop generating infinite power points).
No Range/Extra Range
Limited to specific body part: e.g. defensive power limited to one hit location.
Useable Less Often (e.g. daily or even once-only). (variant of reduced power point cost)
Always On/Uncontrolled Power    -mixed benefits/penalties; may be either an advantage or disadvantage.
Extra fumble effect (usually poorly balanced as a variable cost disadvantage, although "friendly fire" damage becomes worse as damage values increases)
Increased/decreased maximum value  -   decreased value generally a poor balancer - you wouldn't have raised it above the threshold anyway. Increase may be OK, but deliberately leads to "all eggs in one basket" characters.
Focus (Item) - an advantage for generic supers powers. Potentially leads to complications like having some dude stealing your powersuit, so this disadvantage might theoretically lead to other people getting free powers, if not carefully considered. See Tech discussions earlier. A similar disadvantage might be use to require focus "body part" for a power e.g. winged flight might give a character a Focus, since their Flight power could be damaged by called shots.
Mega-Scale-a HERO 6E advantage for massively upsizing an area affected; can be used for speed or range as well.
Usage Limitation (i.e. doesn't work against yellow objects, works only in a specific case) - good for creating more specific powers out of general powers e.g. a generic super-attribute power could be customized to represent anything from dwarf stability (+4 Strength applicable against being moved only) and poison resistance (+4 Con for checks against poison) to . This sort of disadvantage requires fine judgment of how often specific situations arise in costing.
Powered by X: has particularly variable (by campaign conditions) circumstantial effectiveness.
Code of Conduct: perhaps a good one for replicating Silver age type supers, and keeping PCs on the straight-and-narrow.
Linked: value of power must equal controlling attribute. Makes raising powers more difficult, adds attribute-dependence without adding extra value to attribute score for characters who don't have the power. DC Heroes uses this for powers and skills. It also builds on this with a "Mystic Link" power which converts a physical or mental power to a 'mystical' power for 10 points, changing the link attribute from the normal default to 'Aura' (the magic stat).
Random: power is generated randomly.