Most of these can be found in any evil biome, unless noted otherwise.
Fire Gargoyle - small fliers that can throw minor bolts of flame, about the same strength as those of an imp. They otherwise attack by scratching, biting and goring with their horns.
Golem - constructs of rock, flesh and bone. They do not bleed as much and are somewhat resistant to damage. There's a more rare Nitrogolem varient that is the same in most features, but can hurl stronger bolts of flame.
Sabreclaw - metallic constructs. It has an axe blade in place of its right hand, and a blade at the tip of its tail. It mainly attacks by clawing, hacking with its axe blade, or stabbing and slashing with its tail blade. Incredibly deadly to unarmored opponents.
Dead Warrior - tall skeletons. Not entirely mindless - races that use evil animals may occasionally use them similarly to how goblins use trolls, and they will accompany their masters on sieges, armed with various forms of weaponry.
Weredragon - hulking, draconic humanoids. They are more similar to wild animals, however, and can be kept as pets. Aside from having a variety of physical attacks, they can breathe stronger bolts of flame.
Iron Lich - large, rare metallic creatures. They are capable of slow flight. They can shoot bolts of frost to cause blunt damage, shoot bolts of flame to cause bleeding and blistering, as well as release undirected gusts of wind to cause bleeding. Otherwise they merely attack by goring and biting. They explode into flames on death.
Frost Wendigo - humanoid creature made of ice, only found within evil arctic biomes. It can shoot bolts of frost to cause blunt damage, usually two at a time (though cutting off a hand will disable that hand from shooting frost). On death, it becomes a statue made of ice.
Green and
Brown Chaos Serpents - tall humanoid creatures with horns. The only difference between them is that the Brown serpents spit caustic bile, whereas Green ones spit stronger bolts of flame. Both can be used as mounts.
Afrit - flying creatures made of stone. They can shoot bolts of flame at their foes - as they lack mouths, they cannot bite, but they still can gore with their horns.
Marsh Stalker - serpentine creatures found in evil wetlands. They can throw globs of corrosive slime at their foes - aside from that, their talons are sharper and can cause higher damage.
Death Wyvern - a skeletal flying creature. It spits bolts of flame, about the same strength as a Berserk Hunter, and can be used as a mount. Tough to debilitate, but thankfully it is a rare encounter.
Chaotic Beings - the following creatures are all parts of one "race" - they are invaders who will siege your fortress. All of the other Heretic/Hexen creatures are also innately their pets. All of the castes feel no fear.
Beast Ettin - two-headed brutes, they are the most common of the chaotic forces. They learn mace skills at twice the usual rate.
Slaughtaur - second most common caste. These centauroids learn sword and shield skills at twice the usual rate.
Ophidian - horned, snake-like humanoids - as common as the Slaughtaurs. They learn pike and spear skills at twice the usual rate.
Reiver - undead, flying torsos. They can shoot fireballs, as strong as those of an Afrit, and their scratches inflict a weakening effect that temporarily reduces endurance and can cause drowsiness. On death, they dissipate into clouds of red energy, only leaving behind any objects they had in their possession.
Dark Disciple - flying, ethereal wizards, appearing as pitch-black, robed figures. They can shoot magical bolts to inflict blunt damage - aside from that, they are tough to debilitate, as they are beings of energy. On death, they dissipate into a cloud of violet energy that can cause bleeding and blistering to any creatures outside of other chaotic beings.
Chaos Bishop - a similar creature to the Dark Disciples - their robes are green instead of black, and they fire dual bolts of magic energy that cause blistering and bleeding. On death, they dissipate into clouds of green energy, which can temporarily reduce toughness of any non-chaotic being creature.
Maulotaur - rare, tall brutes. They can gore with their horns, and feel no pain - they also have innately higher strength and toughness attributes. They learn hammer skills at twice the usual rate.
Heresiarch - tall, demonic sorcerers. They can fire double fireballs, single magic bolts to cause blunt damage, and increase their own toughness with a barrier - on top of that, they can reanimate corpses as Chaos Bishops. Rare.
Serpent Rider - one of the ruling, most rare castes. These demonic spellcasters can throw bolts of lightning to cause blunt damage, and can temporarily increase their own speed - they can also reanimate dead bodies as Dark Disciple minions. They learn pike skills at three times the usual rate. On death, they dissipate into a cloud of lightning, which can cause paralysis to any non-chaotic being creature.
Death Rider - the other ruling caste - just as rare as the Serpent Riders. These hulking, intelligent beasts throw a variety of projectiles at their foes - stronger fireballs, corrosive bile, magic bolts, frost bolts, and dark energy bolts.
The Chaotic Beings lack some forms of armor, most notably foot and lower body armor. For weapons, they have whips, scourges, serrated swords, two-pronged spears, ceremonial tridents (pike skill), regal staves (spear skill), throwing hatchets, crossbows, spears, short swords, long swords, scimitars, maces, morningstars, battle axes, mauls and war hammers. They will send out both snatchers and thieves to your fortress.