All of these are playable in adventure mode, and live in towns. Note that they are not specific derivatives or crossovers - merely regular horror tropes with my own weirdness thrown in.
Cannibals
Clans of cannibalistic humans were nothing new - however, in the recent years a disturbing trend has appeared, where the clans unite under a single chieftain, and raid the mountainhomes and other settlements. Despite the years of poor breeding and general insanity, they have a high skill in mechanics, making primitive but deadly contraptions.
"Looks like meat is back on the menu, boys!" The Cannibal clans are the lowest tier of invaders, and may harass your fort as early as once you get 20 citizens - for the most part, they are just larger humans who feel no fear or pain, and who are shorter lived. Due to a lack of intelligence, they have forgotten how to make proper armor or shields - as a result, they only wear leather clothing for protection - aside from normal clothes, they have their own pieces, like short-brimmed hats, leather masks, aprons, or sacks they wear on their heads. In terms of weapons, they utilize mostly tools and some simple weapons, along with a few mechanical contraptions - the first being chainsaws, the second being Spike Launchers, a highly deadly ranged weapon type.
They have different "soldier" profession names:
Swords - Skinpeeler, Elite Skinpeeler.
Axes (including chainsaws as well) - Sawyer, Elite Sawyer.
Maces - Meatmaker, Elite Meatmaker.
Pikes - Impaler, Elite Impaler
Spears - Pigsticker, Elite Pigsticker.
Hammer - Tenderizer, Elite Tenderizer.
Whip - Flayer, Elite Flayer.
Their weapon loadout consists of:
Clawed Gloves - dagger-type, may be used by thieves. Beware of the ones with short-brimmed hats, allegedly they can kill your dwarves in their dreams.
Cane and Bush Machetes - sword-type.
Meat Mallet, Clawhammer - small hammer-type weapons - clawhammer is slightly larger.
Spade - spear-type - has a stronger blunt attack, but a slightly weaker jabbing attack.
Serrated Cleaver - dagger-type.
Hewing Axe - axe-type.
Chainsaw - axe-type - particularly deadly, but requires multigrasping for most human-sized creatures. Sawing attack is slower but recovers faster - stab attack is the opposite.
Long Knife - dagger-type.
Mattock - mace-type - edged attack functions similarly to pickaxes - has a blunt handle bash attack too.
Meat Hook - sword type - has a single "hack" attack that is rather deadly.
Crude Pitchfork - spear type.
Spears, Bows, Crossbows - standard vanilla weapons.
Throwing Hatchets - throwing weapons - Cannibals with these will be called "slingers" or "elite slingers". Function like axes, only smaller.
Spike Launcher - a ranged contraption - fires large, crude spikes that are even capable of severing limbs.
Pirates
Cursed seafarers, who after dying at sea were punished for their violent pillaging, rape and murder. The deity responsible for it seems to have done a terrible job at it however, as these scoundrels revel in their undead nature - luckily, they seemed to have completely forgotten what ships are. Unfortunately, they have repurposed some of their old, weathered equipment - some pirates have been seen wielding massive anchors, or even shoulder-mounted cannons as weapons. Worse still, some have turned into mutated, inhuman wretches reminiscent of sea creatures.
The undead Pirate crews are the second tier of invaders - they still do not use metal armor or shields. However, their weapons are more practical for one, and secondly - they have different variants, which are as follows:
Cursed Pirate - the most common variant, they are intelligent humanoids with the same advantages that most undead enjoy, making them tough to debilitate in any way. Same size as normal humans.
Skeletal Pirate - these bony pirates are slightly larger - however, they can only hold objects with their right hand, as their left has been replaced with a metal hook. This obviously makes them terrible at utilizing any ranged weapons - however, the hook itself is also cursed - dwarves who get slashed with it have a chance of getting their strength, agility, endurance and toughness drastically reduced.
Oceanic Hag - female pirate witches - they have eight tentacles instead of legs, and can use two types of spells - they will either cast Aqua Shield on their fellow pirates, quadrupling their toughness, or Water Bubble on their enemies, reducing the speed and agility of the affected creature - on rare occassions, the poor, unfortunate soul encased inside the bubble will begin drowning, their lungs filling up with water.
Snapper Pirate - mutants with crab-like features - the right side of their bodies is covered in a tough carapace, shielding them from attacks. Their right arm in particular is grotesquely enlarged and ends in a pincer, whereas their right eye is actually an eye stalk. Nearly twice the size of a regular human.
Sharkhead Pirate - mutants with shark-like features -they possess a tail, fins, and sharper teeth and claws. Their bites and scratches are much more deadly as a result, and they can lash with their tails. They are very large, slightly more than 10 times the size of a normal human.
Angler Pirate - small, diminutive mutants with features of anglerfish, including a glowing lure. Only slightly bigger than dwarves, they are incredibly fast and agile but also much weaker than other pirates - their bites are also incredibly deadly.
Whale Pirate - truly colossal but rare mutants with the features of a whale, possessing fins and a tail that they can lash with. They are 100 times bigger than an average human. Out of all the pirates, they are the only ones that can carry anchors or cannons with only one hand.
Pirates have a varied set of weaponry - most of which have the "pirate" prefix.
Swords - rapier, sabre, cutlass, spadroon.
Guns (actually use the crossbow skill) - blunderbuss, musket, flintlock.
Shoulder-mounted cannon - fires large cannonballs at a high velocity, but is incredibly heavy and only gigantic beings can use it with one hand. For gameplay purposes, internally it uses the "bow" skill (although pirates using it will be called "Cannoneers" or "Elite Cannoneers" instead).
Boarding Axe - a small axe type.
Boarding Pike - a smaller type of pike weapon, more useful in close quarters.
Throwing Harpoons - harpooners will utilize them.
Shiv - only thieves will use it (pirate thieves are called "Cutthroats" instead).
Spears - regular vanilla spears.
Anchor - uses the mace skill - is incredibly large and heavy, and most creatures cannot use it one-handed. Has a slow attack that can launch most things atleast a few tiles away on a successful impact with the upper or lower body.
Pirate soldier names:
Sword - Swashbuckler/Elite Swashbuckler
Crossbows/Guns - Gunner/Deadeye Gunner
Axe - Pillager/Elite Pillager
Cannon (also bows) - Cannoneer/Elite Cannoneer
Pike - Impaler/Elite Impaler
Spear - Skewerer/Elite Skewerer
Mace - Anchorman/Elite Anchorman
Hammer - Smasher/Elite Skullsmasher.
Recruit - Swabby.
Thief - Cutthroats.
All Pirates additionally can go into a frenzy, which is a self-buff that temporarily increases their combat rolls.
Zombies
A strange plague has swept through many of the formerly allied human kingdoms, zombifying most of their citizens and killing the rest. These new zombies are somewhat intelligent - bearing hazy memories of their former lives, capable of speech and using simple tools and weapons - they often spend time by repeating actions that were significant to them, and are still quite hospitable. A grotesque side effect are the mutations that rarely occur in some individuals, giving them special features...and in most cases, a horribly cunning, evil intelligence that lets them whip up the more simple-minded undead into a frenzied lust for the flesh and blood of the living.
The zombie hordes are a third-tier invader race, capable of using metal armor. They still cannot make shields, and they also do not have any ranged weapons available. As with the pirates, all of them enjoy the same advantages that the vanilla undead do - making them tough to debilitate. Even worse, the special zombies bite attacks are infectious - after a long period, the affected dwarf has a chance of being zombified - the infected dwarves behave more erratically and are more aggressive - the final effect being that they turn hostile to all living beings. Those dwarves aren't quite full zombies - as a result, they still can overexert, and its easy enough to cripple them - however, the zombification is final, and there's no coming back from it.
Variants:
Zombie - the regular zombie is just an undead human. They learn skills slower than most creatures however, and so are not always particularly effective fighters.
Bloated - a mutant, massively swollen with corpse gas. Its intestines have burst through its stomach and also have a fanged maw, allowing them to bite with it - this wont actually infect dwarves. They can release their gas either in an AOE burst or in a single direction - if inhaled, it can cause fevers, coughing blood and vomiting blood.
Retcher - a zombie covered in tumors, with a fluid-filled sack on its stomach. It vomits up flesh-rotting sludge, causing necrosis in those covered with it.
Meatchomper - a large zombie swollen with both muscle and fat - spikes on its spine have burst through its flesh, and it has a bony spike at the tip of its tongue - it is used for stabbing attacks, and sucks out blood on successful hits. They otherwise are a more common heavy hitter.
Snaretongue - tall zombies, with three, elongated tongues, and tentacles at their wrists. They can lash with them - due to how sticky they are, they can latch on to limbs, setting up for shaking attacks.
Oozecrawler - smaller, four-armed zombies. They crawl on the ground and climb walls faster than other zombies. Their hands and fingers are covered in blistering ooze - scratches can spatter it over wounds, causing potentially severe blistering.
Bonegrinder - the largest zombie variant, and the most rare. They are large brutes, with bone plates and sharp spikes on their lower arms and other parts of their body. They can use their arms as clubs, potentially causing very deadly injuries.
The zombie weapon set is a combination of the melee weapons available to normal humans, and some of the cannibals "tool" weapons - they do not use chainsaws, however. Their soldier names are also standard.
Entertainers
Rumors have arose in various taverns, of a strange circus that sets up settlements in various areas. Whoever its workers are, they are not dwarves, humans, elves, or even goblins - they are something much more sinister - few see them up close, and yet fewer live to tell the tale - those who do are often traumatized by the horrible acts of depravity they witnessed; it is not known what happens to the victims of this circus, but children are not safe from it either - many families have seen their children get carried away by diminutive, brightly-coloured monsters. The only consistent descriptions are of an unnaturally tall, human-like figure, nicknamed the Ringmaster - who silently watches from afar, and disappears just as quickly as he appears.
The circus Entertainers are another third-tier invader race - they do not have metal armor or shields, but have a large variety of ranged weapons instead. Their variants also are highly different from each other, and often attack in rather unconvential ways.
Variants:
Clown - the standard, most common members of the Circus. They will pull levers if possible, and learn axe, crossbow and throwing weapon skills faster. They can throw disgusting pies from a distance, potentially causing blistering and bleeding from the acid burns. Clowns can enter a frenzy that gives them a temporary increase in combat rolls.
Mini Clown - a diminutive form of the regular Clowns - they are more agile and run much faster, but are more cowardly, and are also smaller - they additionally have no knees. They possess the same pie toss and frenzy abilities.
Sad Clown - frail, suicidal clowns that are drained of all colour. They can ineffectually spray a tiny glob of water, or cry, which makes the dwarves who hear it more prone to depression and makes them feel sadness. Due to being suicidal, they feel no fear, and recklessly charge into battle.
Strongman - a large brute, resistant to damage. They feel no fear, and are highly prone to rage - they learn unarmed and blunt weapon skills at faster rates.
Bearded Woman - a large creature swollen with massive amounts of fat. They can throw up a stream of caustic vomit, causing necrosis and blistering. They are more prone to rage than most other creatures, but not as much as the Strongmen.
Beast Tamer - a chimeric humanoid, with a scorpion's stinger, the horns of a bull, a boar's tusks, and a shark's fins. They swim faster, and also learn animal training and whip skills at much higher rates. Their stings can inject "laughing venom", which has a chance of causing paralysis, and will always make a dwarf feel amusement - potentially right before their death.
Sword Swallower - a humanoid with metallic blades protruding from its eyes, torso and neck. It walks on two metallic spikes instead of feet. They learn sword skills faster, cannot be blinded, and instead of kicking they stab or slash with their foot spikes.
Fire-Eater - a vaguely draconic humanoid with a pair of horns. They can spit fireballs at their enemies - however, they themselves are not immune to fire, as is shown by their organs being visible through a burnt hole in their stomach and chest areas.
Contortionist - a slime-like humanoid. It feels no pain, does not have to breathe, and cannot be debilitated easily - they lack most organs, only their brain is still present in their chests. Even if their legs are cut off, they are capable of crawling faster than most other creatures. They learn dodging at increased rates.
Conjoined - a humanoid whose twins torso protrudes from their back. This lets them wield twice as many weapons and also see from all directions.
Juggler - a freak with additional pairs of arms growing from its knees, stomach, and mouth. They focus mostly on ranged weapons, particularly thrown ones.
Acrobat - a bat-like humanoid with two pairs of wings - one is attached to their upper arms, the other to their lower legs. They are capable of flight, and learn dodging faster.
Ventriloquist - a strange freak - its main head only has a pair of eyes, but no mouth - its right arm ends in another torso instead of a hand, however its left arm is normal. The secondary torso's head has a mouth with sharp teeth, but no eyes, and a normal pair of arms. The Ventriloquist can make dwarves hear whispers, making them more paranoid and prone to aggressive behavior, even long after a siege.
Magician - a strange humanoid that resembles a hybrid between a rabbit and a dove - it has a toothy beak, and is covered in feathers. They can make dwarves see illusions, which has a low chance of driving them berserk, on top of giving them negative moodlets. Even when unarmed, magicians are highly threatening, as they have circular saws made out of their own bones hidden within their wrists and torso, providing a deadly method of attack.
Magician's Assistant - this poor sap was the assistant of the magician. After an accident, it is now a bisected torso that crawls on tendrils made out of its own guts. Its intestines have a fanged maw allowing for another biting attack.
Puppeteer - a horrid freak with wooden skin - it has a normal, humanoid torso, but its lower body is more akin to that of a spider. They can raise dead bodies as resistant, fearless puppet minions.
Ringmaster - an unnaturally tall humanoid. The Ringmaster himself is only outdone in size by the Strongman. He can use two abilities - the Ringmaster's Roulette, which can randomly cause many different ailments, including zombification of the affected dwarf - or, it can cause positive attribute buffs...maybe not so positive if the dwarf should get them in addition to zombification; his other ability is to raise dead bodies as "backup performers" - evil clowns that function similarly to the standard pie-throwing clowns.
As you might have guessed, the circus freaks use rather strange weapons - a full list:
Barbell - a large, mace-type wepaon, with a slow but powerful bash attack.
Mini Chainsaw - a smaller type of chainsaw - its attacks are no less deadly.
Flower-shaped dart gun - a small ranged weapon - fires tiny, piercing darts.
Throwing knife - quite obvious - they can be rather deadly in the proper hands.
Juggling club - another thrown weapon, this one does blunt damage.
Oversized mallet - a giant clown hammer. Slow to swing, but is devastating when it connects.
BB Gun - rifle-type weapon. Obviously, the freaks redesigned it so its actually quite lethal.
Juggling Ball - they come in two variants. Standard juggling balls do blunt damage - spiked ones do damage more similar to that of a morningstar.
Pole - a blunt spear-type weapon.
Oversized Poker - a pike-type weapon.
Showman's Cane - a mace-type weapon, does severe blunt damage.
Aside from those unique ones, they use a few different types - they also have chainsaws, long and short swords, clawed gloves, serrated cleavers, long knifes, bush machetes, whips, scimitars, spears, and throwing hatchets.
Their soldier names are similar to those of the Cannibals - however, their pikemen are called Pokers/Elite Pokers, whereas their spearmen are called Ticklers/Elite Ticklers.
Skeletons
Some necromancers are not content with merely hiding away in towers - they instead seek out further power, eventually turning themselves into horrid, skeletal abominations. At that point, something seems to take over them, and they raise entire armies of skeletal horrors to take over the world - they seem to have a strange sense of humor, as both they and their minions make various, groan-worthy bone-related puns.
"A vile Army of Darkness has arrived!" The skeletons are the highest tier of invaders, and only have a chance of coming to siege you if you have 110 dwarves or more. They are also by far the toughest, and have a nearly complete set of armor - they use shields, helmets, gauntlets, boots and mail shirts - no breastplates or leg protection, however. All skeletons will "threaten" dwarves will also making horrible puns, making dwarves agitated, exasperated, and also making them more violent.
Variants:
Skeleton - the bog-standard skeleton, nothing special to note - they are the most common.
Giant Skeleton - a gargantuan skeleton, more than ten times larger than a human. As a result, they use most weapons completely one-handed with no penalties.
Pumpkinhead - a skeleton with a carved pumpkin for a head, and vines entwined with its bones. Aside from lashing with its vines, it can launch a single fireball as a ranged attack.
Metal Skeleton - a skeleton made out of metal, with three purely decorative spikes on top of its skull. Resistant to blunt or piercing damage - edged damage works better against them.
Skull Brute - a four-armed, brutish skeleton. It has a decorative tail. They are rather large, though nowhere near as big as the Giant Skeletons.
Skelesnake - a skeleton with a serpent's skull and two pairs of arms. It crawls on its single tail - due to their sharp claws, they can climb up walls and crawl on the ground faster if needed.
Marrow Behemoth - a gargantuan skeleton with a pair of horns, and bone blades at the ends of its knuckles, enabling to be highly dangerous even when unarmed.
Graverobber - a large, skeletal abomination with three pairs of arms and three pairs of legs. It learns the spear skill faster - so they are more likely to utilize spears, shovels and spades - Graverobber spearman are called Diggers/Master Diggers.
Frostbone - an iced over skeleton, with icy crystals growing in some areas. They use two forms of ice magic - either hurling balls of frost as a blunt projectile, or casting a Curse of Frost that causes pain in the muscles and a reduction of speed. It and the two other elemental skeletons are the same size as a regular skeleton.
Blazebone - a charred skeleton. It uses fire magic, either shooting streams of fire, or throwing bolts of magma - thankfully, they're very rare, and can be somewhat of a liability to their fellow skeletons should their allies get caught in their fire streams.
Rotbone - this greenish skeleton is what happens when a skeleton gets bone cancer. They can cast Curse of Rot, which causes necrosis and pain in the muscles, and Curse of Sickness, which induces a fever, vomiting blood and coughing blood.
Bone Witch - one of the two, very rare "boss" castes that also serve as "breeders" - this one is a six-armed, floating torso with a pair of horns. They are larger than even Marrow Behemoths - and can cast Curse of Brittleness, which causes necrosis in the bones, and a reduction of toughness to 50%, and Damnation, which temporarily reduces skill rolls and also makes a dwarf more erratic and violent. They lastly can raise dead bodies as weak, transluscent Lesser Skeletons.
Grave Keeper - an utterly massive skeletal abomination, possessing three heads and four arms - bigger than the Giant Skeletons. Unlike the Bone Witches, which use debuffs on enemies, the Grave Keeper instead buffs himself with either Spirit Shield, increasing his own toughness by 200%, or Deadly Strength, which increases his strength by 200%. He can also raise the same Lesser Skeletons as the Bone Witch - however, in addition to that, he can also breathe a cloud of zombifying gas, that has a low chance of, well, zombifying dwarves, should they inhale it.
Skeletons utilize a very practical set of melee weapons - most of the vanilla weapons are at their disposal - whips, scourges, long swords, etc. They also use spades and shovels, and two unique weapons - instead of pikes, they use wicked scythes, which instead function more like axes, and possess a powerful slashing attack; and spiked wheels, because it wouldn't be right without those - though very large and heavy, their slow smash attack is incredibly powerful, should it connect.