Hello! First time posting here, I've got a project I'm working on and was hoping to get some thoughts, as I'm not particularly skilled at math and probabilities.

I've been toying with an "Xd6 Roll Under with Modifier" (mouthful!) dice system for my game where X is the difficulty of the task determined by the GM, and the players must roll, subtract the Capability's modifier, and the result must be below the relevant Capability Score.

Difficulty for the checks will go from the easiest at 2d6 to the most difficult at 5d6. Players will roll the dice for the check, subtract their Modifier from the sum of the dice, and if the total is below their Capability Score, they succeed.

I'm including the Modifier as a way of incorporating the character's stats into the roll. Modifiers are based on a character's Capability Score, which has a maximum value of 20. The Modifier starts at 0 for a Capability Score of 3, and increases in increments of 1 on odd numbers (Modifier=1 at Capability 5, Modifier=2 at Capability 7, etc. up to a maximum of Modifier=9 at Capability 20.)

What issues do you see with this system? Does using modifiers make actions too likely to succeed? Would this system also work with "to hit" rolls for attacks where Dexterity or Strength are the Capability? I'm trying to keep the kinds of dice required to a minimum, so that's the reason for trying to use a d6 system.

Advice is much appreciated, thanks!

Also, if there's anything unclear, I can include additional information to see if I can hammer things out as I get close to play-testing with some friends.

For probabilities, the site anydice.com is very useful.

Here's an example where I've put "roll 2d6, take lowest of the two." https://anydice.com/program/1ce9f

With your described mechanic, what you'll want to do is write "output 2d6", then click calculate. If you're thinking of a roll under mechanic, then you'll want to know how many of the results are likely to be that number or less, so click "at least" to see that.

For example with 2d6, 100% will be at least 2 (since the lowest you can roll is 1,1 = 2), 83% will be at least 5, 72% at least 6, 17% will be at least 10, and so on.

If you do "output 3d6", then 4d6 and 5d6, you'll see the chances of rolling under a number drop.

As a general comment, I'd caution against novel dice mechanics for the sake of it. If you as the game designer have difficulty with the probabilities, so will the players, and so it becomes just "throw the dice and hope for the best", and tends to make it feel more like a roulette table, very abstract. I know because I've done game designs like that and that's what we found in playtesting - it makes it more of a game than roleplaying.

Xd6-mod less than 'player' capability?

Instead of making the number of dice increase, why not use a scene target number and 2d6-mod?

Then you can adjust the target based on difficulty?

This is what ICRPG uses, except d20.  Target can apply to all in a scene, or you could split it up.  Monsters could have their own target number if you like.

This makes it easier to see what's going on in terms of desired die rolls.

Or you could just borrow a system that everyone knows already.

Quote from: Kyle Aaron on October 09, 2024, 07:34:31 PMFor probabilities, the site anydice.com is very useful.

Here's an example where I've put "roll 2d6, take lowest of the two." https://anydice.com/program/1ce9f

...

As a general comment, I'd caution against novel dice mechanics for the sake of it. If you as the game designer have difficulty with the probabilities, so will the players, and so it becomes just "throw the dice and hope for the best", and tends to make it feel more like a roulette table, very abstract. I know because I've done game designs like that and that's what we found in playtesting - it makes it more of a game than roleplaying.

helpful link! and thanks, i don't want to reinvent the wheel or anything, i think i just felt like i needed novel mechanics. but i think you're right, i should just find a good dice system to use and not make that into another task.

Quote from: orbitalair on October 10, 2024, 12:19:13 PMXd6-mod less than 'player' capability?

Instead of making the number of dice increase, why not use a scene target number and 2d6-mod?

Then you can adjust the target based on difficulty?

yeah, i think a target number system makes sense, thanks!

The Bloodsword gamebook series and I think a lot of the Fighting Fantasy series (Sorcery! is my favorite) use 2d6 dice rolls, you can look into those. Especially Bloodsword was designed to be played with 1-4 players. You have to be aware of the bell curve. For example 2d6 roll under gives you better-than-average chances for a target of 7. Then each +1 improves with diminishing returns, so +1 applied to 6 is much more impactful than +1 applied to 10 for example.

Quote from: Esperado on October 09, 2024, 04:18:10 PMHello! First time posting here, I've got a project I'm working on and was hoping to get some thoughts, as I'm not particularly skilled at math and probabilities.

I've been toying with an "Xd6 Roll Under with Modifier" (mouthful!) dice system for my game where X is the difficulty of the task determined by the GM, and the players must roll, subtract the Capability's modifier, and the result must be below the relevant Capability Score.

Difficulty for the checks will go from the easiest at 2d6 to the most difficult at 5d6. Players will roll the dice for the check, subtract their Modifier from the sum of the dice, and if the total is below their Capability Score, they succeed.

I'm including the Modifier as a way of incorporating the character's stats into the roll. Modifiers are based on a character's Capability Score, which has a maximum value of 20. The Modifier starts at 0 for a Capability Score of 3, and increases in increments of 1 on odd numbers (Modifier=1 at Capability 5, Modifier=2 at Capability 7, etc. up to a maximum of Modifier=9 at Capability 20.)

What issues do you see with this system? Does using modifiers make actions too likely to succeed? Would this system also work with "to hit" rolls for attacks where Dexterity or Strength are the Capability? I'm trying to keep the kinds of dice required to a minimum, so that's the reason for trying to use a d6 system.

Advice is much appreciated, thanks!

Also, if there's anything unclear, I can include additional information to see if I can hammer things out as I get close to play-testing with some friends.

your option looks similar to Odnd, where the player skills are the same number that must be rolled under, that way the stronger is your barbarian, the easier it is to roll under. the suggestion abt the diminishing returns is also pretty apt keep that in mind. anydice also hase some articles on it that clarify some of the statistics behind common dice distributions if i recall correctly

Quote from: Kyle Aaron on October 09, 2024, 07:34:31 PMFor probabilities, the site anydice.com is very useful.

Here's an example where I've put "roll 2d6, take lowest of the two." https://anydice.com/program/1ce9f

This is an incredible resource! Thanks very much. I'm sharing this with my game dev friends.

Thank you everyone for your recommendations and advice, what I've ended up doing is grabbing the check system from the Cepheus engine, which is a 2D6 roll plus modifiers versus a target of 8, and the GM can add difficulty modifiers to the player's check from +6 to -6.

I'm enjoying simplifying the process by trying to go with open source stuff as much as I can, thanks to orbitalair for the suggestion!

I'm not sure if it makes sense to rework what you've got to fit this, but it's usually easier to add numbers than subtract them. I always think about the lightest possible math at the table.

To be honest, you're asking for two math operations (addition of dice and mods, and then subtraction), that is going to wear on some people and kids.  Perhaps you can modify it to a 'roll over and bust' method?  Kind of like blackjack, maybe your get a crit or narrate something cool if you hit the target exactly (like a blackjack.)  For opposed rolls, rolling high loses, and perhaps getting a tie is a 'push' and you and the PC dramatically describe how they trade blows and parry over witty banter.  So, instead of capacity maybe you have capability and your dice pool goes up or down when you have advantages or disadvantage in a conflict.  For example, light armor adds a die and heavy armor adds two dice.

Thank you for the ressource ! I'm a bit nevrotic about statistics. Your link will surely eat a large part of my christmas holidays !