I've only included the monsters that are interesting and/or non-trivial. Some of them are inside PDFs, so you'll have to go through the PDFs to find them.
Aside from that, this is a complete index of all the monsters I've ever posted. It's from all 3 of my settings (Centerra, Eldritch Americana, and Synthexia). Mostly Centerra, though. Nearly all of them have stats, but not all.
I'll update this list as I add more beasties. Last update: 8/8/15.
Adventuring Party, Rival - Five examples.
Alabaster Homunculi - Like marble statues that abduct you.
Alabaster Hound of Yog - Amnesia-inducing, hairless hounds. (Book of Tigers PDF)
Amberino - Tiny electrical buddies for fulgarite elementals. (Book of Mice PDF)
- Chorus - Swarming spirits of the unborn.
- Messenger - Baby-faced cherubs with magic arrows that are depressing to kill.
- Preacher - Winning hearts and minds.
- Sentinel - Too beautiful to wound, these angels brand targets with the "enemy of heaven" rune.
- Wheel - Strange, judgemental creatures with a martyr-maker mechanic.
Animated Barrel - Fond of swallowing people and then rolling down stairs.
Ant, Giant - Includes rules for infiltrating their nest (the only way to make giant ants interesting).
Anomalocaris - Giant predatory shrimp.
Antediluvian Crocodilian - Slouching crocodile born from your own genome. (Book of Mice PDF)
Astral Peacock - Spread feathers force your soul from your body. (Meal of Oshregaal PDF)
Awakened, The - Who have realized the unspeakable truth about the universe. And an adventure.
Bandits - NPCs murderhobos. HD 1, AC leather, sword, bow.
Barnacle Man - Heavy-shelled jerks who live in sea-caves and weaponize sea fauna.
Berserker, Asthmatic - Furious berserkers for a few rounds, then they slow down.
Berserker - Crush! Kill! Destroy! They come in many different flavors.
Beast of Four Sorrows - Melancholy beasts formed from four tragic souls. (Book of Tigers PDF)
Black Wind Tree - Carnivorous tree with mutagenic fruit that controls air. (Meal of Oshregaal PDF)
Blobbins - Blue, boneless goblins who live in jars that they haunt after death.
Blue Breath Devils - Exiles from the planet's inner sun. Smoke creatures that haunt your lungs.
Bomba Bird - Degenerate phoenixes.
Bone Needle Man - Skull-rattling doom skeletons that tap into the Edgeless Sharp (Book of Mice PDF)
Bringers of the Dawn - Formerly Heralds of Immaculate Morning. Cult of the Good.
- High Priests - Peaceful killers, not too different from normal clerics.
Cannon Lizard - Drags a cannon ball in its tail, which it is capable of firing, then re-swallowing.
Cave Clam - Immobile, bubble-spitting maws filled with flying suicide drones.
Cave Cricket - Bite grants infravision, but also light blindness.
Chelinausca - Centipede people. Masters of the morlocks and rightful rulers of the surface world.
Craniac + Ixian Jumping Spiders - Flying heads that barf out spiders.
Crawling Giant - Despondent giants that crawl through the earth.
Cumulonictus - Jellyfish the size of a cloud. Floats in the clouds, plucking up prey. (Book of Tigers PDF)
Daisy Sharks - Related to mosquito larva, adjacent dirt has the consistency of water.
- Bone - Rude demons whose poison causes all of your bones to fuse together.
- Gas - Swallow hope and fart insanity.
- Lemure - You don't roll to see how much damage you do, you roll to see how many you kill.
- Tongue - Size-changing demons that replace your tongue with their bodies.
Devil - These are just demons who have sworn the Oaths. See Demon, above.
Dragoneater - Dire mongooses that excel at killing dragons.
Druhok - The women are mute women, the men are incomprehensibly virile goat people.
Dungeon Barnacle - The only monster in this bestiary with a hooked penis attack.
Dungeon Bug - Tiny pests that can cause people to behave as if they were bugs as well.
Dungeon Dryad - Keeper of the subterranean grove. Includes stats for dungeon plants.
Egg Bearer - Gelatinous tiger with weaponized dreams and an egg inside their body.
Egg of Kioz - Floating metal eggs with time powers and a weaponized youth beam.
Ego Sprite - Figments of your imagination that thrive on popularity.
- Beer - Drunkeness incarnate, it barfs and sometime falls over for no reason.
- Fire - Explodes when killed. Requires fuel.
- Fulgarite - Lightningstruck fused-sand elementals with suicidal tendencies. (Book of Mice PDF)
- Laser - Move tremendously fast and fire many lasers.
Eternal Slug - Zone of slow and swallow attack.
- Candy - Turn your horrible old weapons into sugar.
- Flower - Turn your boring old food into flowers.
- Gem - Turn your shiny gold into awesome glitter.
- Ice - Turn all of dangerous flammables into lovely toys.
- Tooth - Can steal the teeth right out of your head.
False Hydra - Grow out of the sewers and eat people. They live in our blindspaces.
False Star - Pseudostars that abduct people.
Feral Infants - Sufferers of Feral Infant Syndrome. You can't just kill them; they're babies!
Flying Clobstrok - Face-grabbing, cliff-jumping crab-spiders. (Book of Mice PDF)
Flying Flechettia Swarm - Flying flowers that drop like weighted arrows. (Book of Mice PDF)
Flying Snail - Antigravitic shells. Their poison stings take effect later, and all at once.
Fragrant Mother - Huge carnivorous plant with a charming scent an internal dungeon.
Froglock - A former wizard being consumed by a parasitic spell, as they turn froggy.
Frothmonger - Some poor bastard colonized by sentient yeast.
Fungal Angels/Demons - Haters of symmetry.
Fyrinx - Lobsters that live in your stomach and stab your organs if you don't obey them. (I should merge these with jelly-johns. . .)
Gengrigar - Rubbery purple ogres who troll the people they come across.
Ghoul - Corpulent, lively, jocular ex-humans who devour the dead.
- Half-ghoul - People in the middle of the process of becoming a ghoul.
Ghoul Bear - Shuffling, carnivorous, raggy bears with paralytic breath.
Giant, Fungal - Spore-laden suicidal giants full of overheard sentience.
Glommerwhist - Hair spiders. (Book of Mice PDF)
Golem, Coral - Paralytic fists. AC crumbles away as it takes damage.
Gore Police - Produce impossible levels of gore and gain abilities as they take damage.
Gretchling - The mascot of this site! Degenerate goblins with super-cowardice. (Book of Mice PDF)
Guino - Skin-weasels that fuse themselves with your body and shit out babies.
Gurgan - Disgusting, pathetic things that sling curses. Better avoided than fought.
Hagula - Hagfish people that drink blood, masters of freak bioscience.
Hallucigenia - Needle-legged weirdos who try to kill you in your dreams if you kill them.
Helican - Dire pelican what swallows every'un.
Homemade Unicorns - "Unicorns" made through the vivisection of stolen children.
Hoplick - Flailing plant-beast with extreme bitterness.
Hum Sloth - While humming, everyone takes damage for every 10' they move.
Hungry Coffin - Flying metal coffins full of surprises, like an evil, hungry pinata.
Indescribable Leviathan - Giant monster that literally defies description. (Book of Tigers PDF)
Inexorable Beast - Returns when killed with new powers and counters.
Intellect Devourer - Body snatchers with diverse cultures.
Intellect Devourer, Giant Mutant - Prevent both characters and players from using big words.
Ishi-Mishi-Manafa - Pink, spring-dwelling monkeys that win protectors through charm. (Book of Mice PDF)
Jabberwocky - The Questing Beast. An entire quest from a single wandering monster check.
Jiragula - Neon eels that sometimes become invincible, fly, and scream. (Book of Mice PDF)
Knight of Kel Dravonis - Flesh-crafting death knights that compete for the weirdest steed.
Lake Drake - Degenerate dragons that can fly directly from the water.
Mayfly Sprite - Curse-flinging fey that only live for one day. (Book of Mice PDF)
Meat Man - Created by unlucky castings of stone to flesh on statues. Causes obesity on a hit.
Mermaid - They want to gossip and eat manflesh.
Meteor Eater - It's a flying meteor that hungers for the calcium in your bones.
Monkeyrat - Most of the temperate cities used to have rats.
Granger - Subterranean humans bred to be mounts.
Killian - Subterranean humans bred for servitude. Lavish and loving.
Squealer - Juvenile morlocks who run for help.
Stygian - Psychics who can see through walls.
Varicose - Small, climbing, murderous, stabby little bastards.
Mossman - Lumpy ex-humans who can join together and separate freely.
Mudman - Gooey bastards that have a suicide attack.
Mutant Dinosaur Generator - Generates mutant dinosaur.
Noxenswine - Necromantic pig balloons filled with poisonous gases.
Octaro - One of eight corporeal "people" (tentacles) of an extradimensional beast.
- Flying Fusion - Eats people, then fuses them into servants for itself.
Opabinia - Flying threats that bite, run away, then return for a second bite.
Owlbear - They throw themselves from trees during full moons and hock up bone-laden pellets.
Persuadable Maggot - Giant maggot made from rotten meat by villagers. (Book of Mice PDF)
Popkin - Mustachioed rabbits that explode when killed. Glamour pets. (Book of Mice PDF)
Powerman - Level 1 fighter possessed by invincible lightning-warrior spirit from a past age.
Pseudo-Imaginary Dinosaur - Phantasms that rely on being perceived to exist.
- Antagonistic - Hyperadactive shape-shifting jelly. (Book of Mice PDF)
- Atavistic - Fires devolution beams & prevents characters from making smart good.
- Chaotic - Chaos incarnate. Roll on a d20 table each turn to see what it does.
- Retributive - Hyperadaptive attack-shifting jelly.
Quantum Ogre - Splits into two identical ogres whenever it takes damage.
Quillypig - Giant porcupines who teleport spines into their targets.
Revenant, Biomantic - Normal-ish dudes who explode into 4 monsters (muscle, skeleton, skin, ghost) when killed.
Rompers - Giant otters. A Centerran staple.
Royal Cannibals - Subterranean ex-royals with the biology and society of ants.
Sandman - Regenerate on sandy surfaces, save vs sleep if you kill them.
Saprocyte Surfaces - The floors and walls will drink your blood if you stop moving.
Sarcosyrinx - Flying gulp-eels who are more invisible the better you know them. (Book of Tigers PDF)
Shade - Undead who wreathes your vision and memories in shadows. Darkvision is a bad idea.
Shadow Child - Shadow archers who pin your shadow to the floor and devour it.
Siege Monkey - Huge things like stegosaurs that throw stones with their tails.
Sinister Folk - Eerie fey than can only be seen in your left eye.
Skeleton Hero - Four arms, four scimitars, and a counterattack if you miss him.
Skeleton Jelly - Shitty skeleton-dude who is immune to damage.
Slime, Catapult - Normally standard ooze that throws chunks of itself.
Slime, Faffernacky - Supernaturally delicious ooze compels you to eat it.
Sludge Vampires - Intelligent, blood-draining, skin-wearing oozes.
Songful Bagman - Sac-like eyeball bastards who lure birds into their stomach through song. (Book of Mice PDF)
Spazbat - Twitchy teleporting bat that drinks your blood by teleporting it into its stomach.
Steeds - Orns, Witch Weasels, Bottled Steeds, Faerie Horses, and Jellybears.
Stirge - Flying, flaccid bloodsuckers. Includes rules for dungeon honey.
Succubus - Ancestral ghost determined to spread the semen of a living relative.
Terophidian - If I ever write a Centerra bestiary, this guy is going on the cover.
Tortoise Tsar - Despotic dungeon kings and quest givers.
Trilobite - Crawling biters that carrying a disease that turns you into a trilobite.
- Green - Rubbery, regenerating bastards. Full write-up.
- Longtail - Become as weak as a child if their tail is grabbed. Full write-up.
- Rock - Petrified by light. Full write-up.
- Rock, Elder (Galeb Duhr) - Can animate boulders. Full write-up.
Tubular Peacock - Nozzle-headed slug-birds that sometimes barf green slime.
Tumble Melon Tree - Melon-lobbing trees that rely on you eating their healing fruit.
Tunnel Snake - Burrowing cave snakes with death breath. (Book of Mice PDF)
Turbo Grub - Cross between a rot grub and that rabbit from Monty Python.
Tuskman - Chaos viking with walrus tusks and other mutations.
Undead Vikings - Exactly that.
Unicorn Addict - Pacifistic weirdos who have eaten too much unicorn dung.
Vampire - Pathetic victims of a disease.
Vector Skeleton - Wireframe creatures that frequently glitch out.
Volguloi - This is what happens when worms eat wizard brains.
Wicked Jelly-John - Alien rat-things that want you to eat them. (Book of Mice PDF)
Wise Parasites - Prophetic insects that parasitize dust drakes.
Witch's Laundry - Animated attack clothing that animates the clothing you are wearing.
Wiwaxia - Prehistoric spine chucker. Like a wyverns tail that crawls.
Wizlocks - Degenerate wizard-gnomes.
- Bolgen - Size-changing tapeworms. (Book of Tigers PDF)
- Corpsegrinder - Barf acid and bones. Hunger for undead. Purple worm replacement.
- Fangolian Ear - Learn their name and they'll grow in your brain. (Book of Mice PDF)
- Labial - Wall-bursting blood-kissers.
Yoblins - Filthy, fungal goblins with a strange life cycle.
Zondervoze - Supersentient creature made up of unwitting, normal humans. A zeitgeist.