So I'm currently putting together some hacks and bits and bobs for running a gritty, dark fantasy game (think Thieves World, Black Company and Dragon's Dogma).

At the moment I'm focusing on making a beastiary, wand id like some suggestions - with a few caveats:

• Monsters are Monstrous - I'd rather not have too many monstrous humanoids, and those that do exist are more like NPCs, with culture and the chance of trade and parlay. If its a monster, it should be weird and beastial.
• Monster Are A Big Fucking Deal - if theres a monster somewhere, its not gonna be hiding under a dungeon and never seen - there should be some nice ecological effects that can be added, though that's mostly flavour. I figure if there is something that can be represented mechanically, I'll steal the Lair and Regional effects from 5e.
• It's an E6 game - so I'd prefer CRs under 5. There's a ton of those, but the issue is that so many of them seem to be pretty mechanically... Meh. Things with interesting mechanics and gimmicks that make for a good fight are the plan here.

I'm happy reskinning things to fit the setting, but if you guys have any suggestions, feel free to tell me what you have or would do with them.

So - any ideas? I'll post up what I've got as I work on them.

Mord'hu, Demon Bear of the Howling Wastes

Spoiler

Mordhu CR 6 XP 1,200
N Large animal
Init +3; Senses low-light vision, scent ; Perception +8
AC 20 (+3 Dex, +8 natural, –1 size)
hp 47 (5d8+30)
Fort +10, Ref +7, Will +4
Speed 40 ft.
Melee 2 claws +9 (1d6+7 plus grab), bite +9 (1d6+7)
Space 10 ft.; Reach 5 ft.
Str 25, Dex 17, Con 13, Int 3, Wis 16, Cha 10
Base Atk +3; CMB +11 (+15 grapple); CMD 24 (28 vs. trip)
Feats Endurance, Run, Skill Focus (Survival)
Skills Perception +8, Survival +7, Swim +16; Racial Modifiers +4 Swim

Twigs snap behind you, after hours of silent trekking. A massive shape crosses through the mist, and then disappears - for a time.

The next time you see it, the creature bursts forth from the fog, bristling with the hilts of weapons driven into its hide, caught in mangy, matted fur. The stench of blood and old battles swiftly follows it, and its rorar echoes with the clash of ancient steel.

An Advanced Brown Bear (CR 6), designed to be a legendary creature of the area and a big battle, possibly to clear the Howling Wastes of the taint that has overtaken them.

(And yes, it's directly lifted from Brave, but come on - its awesome).

Jardín de Estatuas

UNESCO World Heritage site in Iberia (because fucking everything in Iberia is an UNESCO World Heritage site...), where the fabled Medusa tends to her flock of cockatrices. Has been collecting statuary for millennia, so a wide array of period correct "carvings" are interspersed here. The pleasant arid Mediterranean climate preserves the statues from excess erosion. Supposedly she and her pets winter in the Balearic Islands, but who knows when she returns.

(cockatrice are low CR level in 5e...)

I like the idea, but the issue is in E6, un-petrifying someone would require a ritual spell, of it was doable at all. I'd maybe take the 4e approach and give three saves, each failed saves adding more penalties, until the third save is full petrification. Then allow for lesser cures (alchemically treated cockatrice blood, a new spell etc.

The Jagdtier (Hunting Beast)

A Rage Worg, recast as a singularly large, unusually intelligent and corrupted wolf-dog who stalks the slums of a large city, living off scraps and the odd meal of homeless stragglers.

With two levels of Barbarian, the Jagdtier gets some nice extra mechanics to throw into the fight, and make sure its a tough fight, and the No Escape Rage Power means the PCs aren't even safe if they decide to run for it!

The Windigo - CR 7

Spoiler

The Windigo CR 7 XP 3,200
CE large humanoid (giant)
Init -1; Senses Darkvision 60 ft, low light vision, perception +6  
AC 17 (+5 armor, +5 natural, +1 Deflection, -1 size, -2 rage)
HP 104
Fort +14, Ref +1, Will +3; +3 vs. spells, spell-like, and supernatural effects while raging
Defensive Abilities Uncanny Dodge, Trap Sense +1, Superstition +3  
Speed 40 ft (50 ft base)
Melee Claw +17/+17 (1d8+10/1d8+10), bite +17 (2d6+5)
Ranged bone javelin +6/+1 (1d8+8)
Space 10 ft.; Reach 10 ft.
Special Attacks Lesser Beast Totem (Rage Power),  Rage 14 rds
Str 30, Dex 8, Con 23, Int 8, Wis 8, Cha 7
Base Atk +7; CMB +18; CMD 27
Feats Iron Will, Power Attack, Toughness, Improved Natural Attack (bite)
Skills Acrobatics +4, Climb +19, Perception +6  
Languages Giant
Combat Gear Bone Javelins (4)

Thicken Ogre Barbarian 4 - with the Superstition and Lesser Beast Totem Rage Powers, combined with the Thicken bite attack, makes for a huge , tough as nails people eater.

This thing lurks on the edges of wilderness settlements, scavenging humanoid carcasses and attacking small groups of travellers when the opportunity arises. Rumours of this creature place it ranging across the wilderness, seeming to settle for a few months at a time before moving on to new pastures.

K'tsichi, Elder Thing

Spoiler

K'tsichi The Watcher CR 9 XP 6,400
LE Huge aberration (aquatic, chaotic)
Init +9; Senses darkvision 60 ft.; Perception +14
Aura mucus cloud (5 feet)
AC 20 (+1 Dex, +11 natural, –2 size)
hp 84 (8d8+48)
Fort +8, Ref +5, Will +11
Speed 20 ft., swim 120 ft.
Melee 4 tentacles +10 (1d6+5 plus slime)
Space 15 ft.; Reach 15 ft.
Str 20, Dex 12, Con 22, Int 15, Wis 21, Cha 21
Base Atk +6; CMB +13; CMD 24 (can't be tripped)
Feats Improved Initiative, Iron Will, Lightning Reflexes, Weapon Focus (tentacle)
Skills Bluff +13, Intimidate +16, Knowledge (Arcana) +13, Perception +21, Spellcraft +13, Sense Motive +10, Swim +24; Racial Modifiers +8 Swim

SPECIAL ABILITIES

Ability Healing (Ex):  Heals 1 point of ability damage per round in each damaged ability score.

Fast Healing (Ex): fast healing 5.

Immunity to Mind-Affecting Effects (Su):

Immunity to Disease and Poison (Ex):

Dimension Door (Su): anywhere within its sanctum

Bound to its domain, but can use PSA's outside of area.

Mucus Cloud (Ex)
While underwater exudes a cloud of transparent slime. All creatures adjacent must succeed on a DC 20 Fortitude save each round or lose the ability to breathe air (but gain the ability to breathe water) for 3 hours. Renewed contact with mucus cloud and failing another save extends the effect for another 3 hours. DC is Constitution-based.

Slime (Ex)
A creature hit by a tentacle must succeed on a DC 20 Fortitude save or skin and flesh transform into a clear, slimy membrane over 1d4 rounds. The creature's new "flesh" is soft and tender, reducing its Constitution score by 4 as long as it persists. If the creature's flesh isn't kept moist, it dries quickly and the victim takes 1d12 points of damage every 10 minutes. Remove disease and similar effects can restore an afflicted creature to normal, but immunity to disease offers no protection from this attack. The save DC is Constitution-based.

Psi-Like Abilities (ML 13th, concentration +16):
At will - Disable (50 ft., 16 HD, DC 20), false sensory input (5 creatures, DC 16), mental disruption (20 ft., 2 rounds, DC 16), mindlink (unwilling, 8 creatures, DC 14)
3/day - Ego whip (ML 7th, 2d4 Cha, DC 17), id insinuation (ML 7th, 3 creatures, DC 17), mind control (all types, 2 creatures, DC 20), thought shield (SR 24, 11 rounds)
1/day - Memory modification (DC 17), remote viewing (speed 40 ft., DC 17), wall of ectoplasm

Pardon the massive stat block, but after eyeing the original Aboleth stat block, I wanted something a little more unique. I followed a conversion to replace the Aboleth's spell-like abilities with Psionics (something that isn't a PC option, but might show up in the weirder monsters), and added the Divine Guardian template (well, most of it).

That template is pretty whacked out, though - +1 CR for a bundle of SLAs, a bunch of immunities, and doubling all its speeds? Seems pretty generous to me.

I left out the SLAs due to their divine origin, and reliance on the alignment system.

But otherwise, it helps create a powerful, almost god-like creature (in E6, at least) that can use its abilities to make multiple problems for the party before they even reach it, then make the fight a living hell.

The Rookwynd Ghul - CR 4

Spoiler

The Rookwynd Ghul CR 4
XP 1200
NE Medium undead
Init +2; Senses darkvision 120 ft., scent; Perception +10
Aura desecration 20ft
AC 19 (+2 Dex, +7 natural)
hp 23 (5d8)
DR 5/magic
Channel Resistance +4
Fort +1, Ref +3, Will +7
Immune undead traits
Speed 30 ft.; four-footed run
Melee bite +8 (1d6+5 plus feed), 2 claws +7 (1d4+5)
Special Attacks charging trip, diseased pustules, feed
Str 21, Dex 15, Con —, Int 12, Wis 14, Cha 13
Base Atk +3; CMB +6; CMD 16 (20 vs. trip)
Feats Weapon Focus (claw), Scent of Fear, Creature of Darkness
Skills Climb +13, Perception +10, Stealth +10, Survival +7
Languages Common

SPECIAL ABILITIES

Aura of Desecration (Su)
The Rookwynd Ghul constantly project an aura in a 20–foot radius that functions as a permanent desecrate spell. The DC to resist negative channeled energy within this area gains a +3 profane bonus. Undead within the area (including the Ghul) gain a +1 profane bonus to attack rolls, damage rolls, and saves. Summoned or created undead that appear in the area gain +1 hit points per HD.

Charging Trip (Ex)
If the Rookwynd Ghul hits with its bite after making a charge attack on all fours can attempt to trip its opponent (+4 bonus). This trip does not provoke attacks of opportunity.

Command Undead (Su)
The Rookwynd Ghul can command or rebuke festrogs as a cleric with the Command Undead feat equal to its current Hit Dice.

Create Spawn (Su)
A creature slain by The Rookwynd Ghul rises in 1d4 minutes as an undead creature of the same type as the undead lord. Spawn are under its control.

Diseased Pustules (Ex)
When The Rookwynd Ghul takes damage from a piercing or slashing weapon, some of its boils rupture, squirting the attacker with puslike fluids. The noxious secretions carry a potent contact disease that causes those infected to break out into painful necrotic boils.

Necrotic Boils: Disease—contact; save Fort DC 11; onset 1 day; frequency 1/day; effect 1d4 Con; cure 1 save.

Feed (Su)
Every time The Rookwynd Ghul makes a successful bite attack, it feeds on its opponent's flesh and gains 5 temporary hit points. The festrog cannot have more than 5 temporary hit points gained by this ability at one time.

Four-Footed Run (Ex)
The Rookwynd Ghul can run on all fours at speed of 50 feet if it doesn't hold or carry anything in its hands. When running on all fours, it is treated as if it had the Run feat.

Spell-like Abilities: 1/day—darkness, fear. CL 5. DC 15

The Rookwynd Ghul is a creature of pure darkness and evil - the bearer of a plague which has the small town of Rookwynd. Now a ghost town, Rookwynd crawls with festering, animalistic undead, with the Ghoul seeming to lead them on raids against neighbouring towns and, in time, cities.

A nice mix of gangs of festerogs, and giving one the Undead Lord template means that the monsters can act in concert and create a roving band of terror and disease. Good times all round.

Pretty awesome thread, in terms of ideas.  If I didn't say it before, welcome to theRPGsite!

You'll excuse the lack of stat blocks - I'm a bit rusty with 5e/3e, lazy and originally made these for AD&D.

Bahampalut, Demon of Perverse Fertility:

A figure that resembles an unholy union of a giant scorpion and a beautiful elven maiden, this creature of darkest Hell thrives on human greed. Wherever it appears, it radiates an aura of fertility that affects nearby area - crops bear harvest 5 - 6 times a year, fruit trees bend under the weight of ripe fruits, forests bear plenty of game, and children grow healthy and strong.

As long as you are willing to provide ample offerings of flesh, so that Bahampalut may grow his own perversion of a family. Usually manipulating a lost traveller, or perhaps a bit over sensitive soul in dreams to become it's priest, if the locals refuse to sacrifice to the cult, suddenly the earth grows barren, animals turn into vile freaks, and children are born with great defects. More often than not, greed prevails - after all, who is going to miss a few poor travellers that pass through the village, or old people on brink of their death? Which is the most dangerous perhaps point of Bahampalut presence - he does not rely that much on his/her demonical spawn to kill you. It lets villagers that worship him drug adventurers and deliver them to it's lair as sacrifice.

The spawn of Bahampalut is created by impaling the victim with it's large, poisonous string, which, while poisonous in it's own accord, also serves as an ovipositor. Then, the victim is wrapped in a gentle cocoon, which is connected by an odd, tentacle - like appendage to the centre of Bahampalut's cavern, where a huge, blobesque object pulsates and pumps nutritious fluid to all of Bahampalut's children. The entirety of Bahampalut's hideout is a vile place, with grass and moss having turned into flesh - like objects, cavern walls covered with veins that seem to be pumping some odd blood - like ichor throughout the whole cavern, mouths suddenly appearing on the floor, all adding to an odd feeling that you are walking in some huge beast's mouth.

When they hatch, the children resemble a grotesque version of the species from which they hatched - some are humans with their joints flipped, walking on all four with large tails finishing with a string that resembles a halberd's blade. Others will grow into creatures made of chitin and claws, or perhaps a simply gargantuan blob of flesh with ten legs and twenty long, whip - like tails.

Bahampalut usually avoids combat, letting his spawn take care of it, but when necessary, the demon opens with trickery - it'll appear to be a beautiful elven maiden, stuck in a cocoon, and as one approaches to free her, it'll burst and attack the tricked adventurer.

Do tell about your current setting as well - I profess a huge love for Black Company as well as Malazan Book of the Fallen (2 works that I think had the biggest impact on my fantasy RPGs, even if both suffer from We Should've Ended Them When They Were Cool syndrome)

From my current Call of Cthulhu campaign, but easily transferable to fantasy. Just stick a layer on demon...or change him into a shapeshifting cultist. An enemy to engage on a more social level rather than haunt the wastes:

Fantastic Mister Wilde and his Amazing Cat

Most monsters avoid living in huge cities, but that is not the case for Mister Wilde. A demonical shapeshifter by nature, sent by Ancient Evil God (for me it's Hastur, but insert Evil God of your choice, of course) to infiltrate the Known World centuries ago. As he tasted the joys of mortal life and feed off their fears, he has become a bit lax in duties...but every now and then, he engages in a dangerous game, intent on awakening his sleeping master, and let his demonical armies conquer the Known World. The only limit of Wilde is that, due to his nature, he is forced by an ancient accord of gods and demons to not directly bring about his Master's rise - for example, he might kill someone who seeks to undo his plan, but he might not try to directly obtain an artefact necessary for awakening his Evil God. And even the former brings about the risk of intervention of other divine parties, one of the few things he fears to fight.

But until the day of his Master's rise comes, he lives in the biggest city of the Known World, enjoying his immortality and building the single largest network of crime, grafting and espionage in the city. Under a moniker of "Repairer of Reputations", he does exactly what it says on the tin - helps anyone who has the money, to solve and shush any scandal, using his wide connections as primary kingpin of the city. And of course, his prices are very, very reasonable - at least while money is concerned, because once you are in his pocket, you are there forever, or he will make your life living hell, before you take it from you. Nobles, knights, merchants, wives and priests - everyone whose life and public office depends on reputation, might one day find themselves in his inviting pocket.

In his human appearance, he looks like a bizarre creature, a dwarf with fake wax ears and many claw - made scratches on his face. His eyes suffer from heterochromia, and he seems to be missing all fingers from his left hand, a crippling injury that he does not make any point in hiding however. Was he ever to assume a true form, he grows to a huge ogre, a true general of Hell, three meters large in size, with blue skin and burning yellow eyes, with his scars shining in crimson red - though there are still no fingers on his left hand. Not that he needs it to wield a large sword with his unholy strength any way. However, each moment spent in his true form, greatly drains him, due to the accords binding him to the Known World - so he prefers to leave fighting to his thugs and pawns. Or when the things get really tough, to his cat.

The Cat of Mister Wilde seems to be the source of his many scars, and itself appears as a bizarrely huge cat, the size of a medium dog, yet not fat like usually large cats are, but made purely of muscle. Covered in white fur with black stripes, it is actually a fallen servant of a Cat Goddess (or any Good God connected with cats or such), who has rebelled millennia ago. It can change to a humanoid form at will (statistics of weretiger, I'd suggest, or werepanther), with claws that put most daggers to shame. Why it serves as Wilde's muscle is a mystery to many, but one thing is certain - the two are most definitely not very friendly, as the scars on Wilde's body are most definitely made by Cat's claws.

Bloodhound

Wise old villagers say, that when a beaten dog of a vile master rebels and tastes human flesh of his abuser, and is not put down, transforms into this beast by the light of a next full moon.

The creature seems to resemble a very large dog, about meter and a half long and a meter tall, with it's fur seemingly glued together with dirt into large clumps. However, a closer examination reveals that it's no fur at all anymore, but a sort of fungi - like carapace, that seems to glow with odd, veiny, crimson energy. The teeth of the beast seem to have grown threefold, too large to ever allow it's jaw to be shut close.

The monster itself prowls the outskirts of villages and towns, hunting down solitary travellers and feasting on them. Yet those who die to it's jaws are the lucky ones - for the survivors who have been bitten, fall within the time of three days into an odd, feverish coma. Then, as the light of next full moon comes, they raise from their sickbeds, seemingly fine...until they try to eat, discovering a hankering towards human(oid) flesh, that will drive them insane, and onto the path of ghoulhood.

Rat Emperor

Everyone knows the old sewerjack tale of the Rat King. But what happens if that odd creature survives it's trials and tribulations, and ventures into the cracks in the sewers that leave to places best not discovered?

It all started in a city built upon ancient ruins of a forgotten race, where sewerjacks started to disappear in great numbers. An expedition was formed, with city watch's man at arms joining the ranks of the smelly sewer workers. Thirty men went in, five returned, pale and with hair turned grey. In afraid voices, they spoke of what they found, first to their superiors, than to the tavern crowds, with neither finding their tale too believable, but spread amongst the gossiping clerks and drunks.

They spoke of a great mass of fur, eyes and entwined tails, a blob of scurrying flesh fashioned of hundreds, no, thousands of rats that squicked in unison as it approached, capturing any rat in it's path and adding it's flesh to the ranks that formed it's bloated, cube - like body. Whenever one tried to strike that monstrosity, it suddenly reformed, revealing a soldier's skeleton picked clean, with it's breastplate taking the hit, or perhaps an old discarded cooking pan that served as a temporary shield, soon disappearing again within the writhing mass, as did the attacker, for the Rat Emperor does not bother to lash out with iron or claws - it simply moves forward, like a wave of the sea, consuming everything in it's path and adding the remains to it's vile body.

And while the denizens of that particular city might for now laugh at that tale, everyone does start to notice there are less and less rats and cats about...yet at night, as you walk the street, you can sometimes hear a great rodent squick beneath your feet.

The Hangman

Nobody is certain how this terrifying undead originally came to be. Some say he was a brave soldier unjustly executed for cowardice in mass execution to make an example. Others, that it is a woman who has been hanged thrice, and should have been allowed free to go, but was hanged again by a cruel lawman. The most popular theory claims however, that it was a bloodthirsty inquisitor, finally sentenced to death by his own men, who struck a deal for vengeance with demons as he dropped from the gallows.

Whatever version is true, should one see a ragged, limping figure with rotting remains of a rope around it's neck and fresh coils of finest silken cordage wrapped around it's body, the wisest thing is to run, as no common blade can touch the cursed flesh (magical blades weren't yet ever tried, as this undead stalks lonely frontier villages rather than castles or metropolises, where heroes possessing such could be found).

As it enters such a village, it's first act is to hang a sheriff, guardsmen, lawmen - whoever is keeping up the order in town. Then, it paints a sigil on the corpse of a lawman it killed, and suspends it in the middle of the town. Any mortal who gazes upon it must be of a strong will, or is hypnotised by it and can not leave the town until the "trial" ends - in fact, such enchanted mortals will attempt to capture anyone leaving the borders of the village.

The trial itself is a farce, where all the sins of hexed villages are uttered by the hoarse voice of the Hangman, as one by one the villagers are sentenced to death for them, with nobody stopping the foul massacre.

The morning after, only death reigns in the village, as the unfortunately traveller will discover purple faces of Hangman's victims...who slowly start to stir to life and cut themselves free, walking off into the night to continue the work taught to them by their creator.

Rincewind1 - awesome ideas!

The setting is similar to Italy circa the 14th century - human dominated (I'm still undecided as to the non-human races, but few will be available as PCs) warring city-states (both internally and with intruders at their borders), and a single monolithic religion to keep everyone tied together, but with enough flexibility to allow for plenty of quibbles and skirmishes over it.

The biggest threats will be mostly mundane in nature, but under the veneer of normality there's always something weird. Most monsters are unique, coming from a variety of sources. Magic exists, but is jealously guarded by mages who worm their way into positions of influence and commit atrocities to attain greater magical knowledge.

PCs are mostly mercenaries, outcasts, and those with nothing left to lose. Should they gather enough power and resources, they can buy themselves a place in the nobility, but they will just end up swapping the toil of adventuring for the horrors of war and politics.