Mythical Monsters

If children do not listen to their parents and they forget to latch their windows at night, the Oni, demonic ogres with the power of invisibility will sneak in and steal away those bad children. We know the Oni are especially fond of eating those children starting at their toes and taking small bites because to them the screams of bad children is music to their evil ears.

- An old grandmother near the Ogre Blight instilling the proper fear in a group of children.

The following list is used to illustrate what creatures and monsters are commonly known to exist, which ones are believed to exist, which ones are believed to be legends/myths only. If the creature does not appear on this list, then it likely does not exist in Oayr neither as a real creature nor a legend/mythical one.
It should be noted that some of the Mythical creatures must truly not exist in order to ensure this list doesn't represent a meta list of real monsters. In addition there are certainly monsters no one has heard rumor of, and the lore of those monsters that do exist will not always stay true to the legends told about them. I.E. There is no way for a player to know for certain that fire/acid affect Trolls or Silver affects Werewolves. Those entries that say common knowledge will for the most part follow the 5e Monster Manual I.E. it can be assumed that it is common knowledge that holy water will affect undead as described in the source material.

Anything not listed here is either so obscure no stories are told about it...maybe it does exist, maybe it doesn't...or I forgot to list it.
Believed to exist somewhere (common/commonly doesn't mean it is not rare, just that it is commonly accepted as REAL)

** Prefix indicates a unique creature to this setting

Animated Armor (construct) Commonly used to protect vaults
Ankheg (monstrosity) Common in hills and forests
Axebeak (monstrous critter) Common in plains and savanas
Banshee (Undead) Rare but believed to exist
Bloodhawk (Hostile critter) Common in jungles/rainforests
Behir (monstrosity) Common enemy of Dragons, hunter of dragon nests/eggs
**Clydoc (Giant 8 legged horse) Common mounts for Woedkin
Bugbear (humanoid (goblinoid) Common created during Undead War by the Tomb King
DIRE ANIMALS (Monstrosity) Common knowledge that freakishly large versions of many creatures exist.
Dragons Common knowledge they exist everywhere
Dryad (fey) Common knowledge they exist Feywild
Elementals Mythical for natural occurring, common knowledge magic users can summon.
Fire Beetle (monstrous bug) Commonly known to exist, unusually large varieties are rumored to exist.
Flying Snake (monstrous critter) Commonly known to live in tropical locations especially islands
Flying Sword (construct) Commonly used to protect vaults/dungeons
Ghast (undead) Common knowledge
Ghost (undead) Common knowledge
Ghoul (undead) Common knowledge
Giants (giant) Common knowledge mountains/foothills
Goblin (humanoid (goblinoid) Common created during Undead War by the Tomb King
Golem (construct) Commonly used to protect vaults/dungeons
Gorgon (monstrosity) Commonly used to protect vaults/dungeons
Hag (Fey evil witch) Commonly believed to be real, even without actual proof. No one doubts these Fey witches.
**Hermit Grub/Snatchwing (Monstrosity) Known to exist large versions rare deep forests/jungles/blighted areas.
Hobgoblin (humanoid (goblinoid) Common created during Undead War by the Tomb King
Homunculus (construct) Commonly used to protect vaults/dungeons
Invisible Stalker (elemental) Commonly used to protect vaults/dungeons
Lich (undead) Common knowledge
Lizardfolk (humanoid (lizardfolk) Commonly known to exist swamps
Mammoth (Big creature) Exists in cold tundra regions of Holmstad
Mephit (elemental) Mythical for natural occurring, common knowledge magic users can summon.
Mummy (undead) Common knowledge
Ogre (giant) Common created during Undead War by the Tomb King
Ogre Zombie (undead) Common knowledge
Oni (giant) Common created during Undead War by the Tomb King
Orc (humanoid (orc) Common created during Undead War by the Tomb King
Owlbear (Monstrous creature) Common knowledge
Roc (monstrosity) Common knowledge mounts for moonsilver raiders from Kenkori
Sauhagin (Fish people) Common along freshwater coasts and wetlands
Shadow (undead) Common knowledge
Shambling Mound (Monstrous Plant) Believed to live in ancient forests/swamps
Shield Guardian (construct) Commonly used to protect vaults/dungeons
Skeleton (undead) Common knowledge
Specter (undead) Common knowledge
Vampire (undead (shapechanger) Common knowledge Athansia
Wight (undead) Common knowledge Athansia
Will-o’-Wisp (undead) Common knowledge Swamps/Forests/Cemetaries
Worg (Magical beast) Common knowledge forests, hills, mountains
Wraith (undead) Common knowledge Athansia
Wyvern (dragon) Common knowledge anywhere...**travel and hunt in family packs like wolves :P
Yeti (monstrous humanoid) Commonly believed to exist in artic mountain regions
Zombie (undead) Common knowledge Athansia

UNCONFIRMED CREATURES, MYTHS, and extinct or banished creatures

Azer (elemental) Rumored to exist in the Emberblight
Basilisk (monstrosity) Mythical
Black Pudding (ooze) Mythical underground/swamps
Angel (celestial) Mythical believed extinct or banished
Blink Dog (Magical Beast) Mythical
Bulette (monstrosity) Mythical in regions of plains/deserts
Centaur (monstrosity) Mythical Feywilds
Chimara (magical beast) Mythical most legends are along the mountains of the western continent Holmstad
Cloaker (aberration) Mythical underground
Cockatrice (monstrosity) Mythical forests
Darkmantle (monstrosity) Mythical underground
Demon (fiend (demon) Mythical believed extinct or banished
Devil (fiend (devil) Mythical believed extinct or banished
Displacer Beast (Magical Beast) Mythical
Dragon Turtle (dragon) Mythical oceans
Gargoyle (elemental) Mythical abandoned cities, cemetaries
Gelatinous Cube (ooze) Mythical underground/swamps
Genie (magical humanoid) Mythical tied to magical items
Gray Ooze (ooze) Mythical underground/swamps
Griffon (monstrosity) Extinct since Undead Wars
Harpy (magical beast) Mythical creature similar to sirens thought to be tales to scare children and sailors.
Hell Hound (fiend) Mythical believed extinct or banished
Hydra (monstrosity) Mythical swamps
Kobold (humanoid (kobold) Mythical underground
Kraken (monstrosity (titan) Mythical ocean strongly believed to exist
Manticore (monstrosity) Mythical forests foothills of mountain ranges
Merfolk (humanoid (merfolk) Mythical oceans
Merrow (monstrosity) Mythical oceans
Mimic (monstrosity (shapechanger) Mythical dungeons/wizard creations
Nightmare (fiend) Mythical believed extinct or banished still believed to be present in Feywilds
Ochre Jelly (ooze) Mythical underground/swamps
Pegasus (celestial) Mythical extinct since Undead War believed to exist in Feywilds still
Pseudodragon (dragon) Mythical Feywilds forests
Purple Worm (monstrosity) Mythical underground
Remorhaz (monstrosity) Mythical underground
Roper (monstrosity) Mythical underground
Rust Monster (monstrosity) Mythical underground
Salamander (elemental) Mythical Emberblight
Satyr (fey) Mythical Feywilds
Shrieker (plant) Mythical underground/swamps/dark forests
Sphinx (monstrosity) Mythical guarding treasures/magical features landmarks
Sprite (fey) Mythical Feywilds
Stirge (beast) Mythical forests/swamps/caves
Succubus/Incubus (fiend (shapechanger) Mythical believed extinct or banished
Treant (plant) Mythical Feywilds
Troll (giant) Mythical dark forests mountain foothills believed extinct during the Troll purge
Unicorn (celestial) Mythical believed extinct or banished still believed to be present in Feywilds
Violet Fungus (plant) Mythical underground/swamps
Werewolf (humanoid (human, shapechanger) Mythical Forests

THINGS THAT SHOULD NOT BE... and just don't exist

All animorphic humanoids. No furries, no Kenku, Tortles or rabbit people.

Cyclops (singular creature rumored to have existed but was destroyed as an abomination)
Dopplegangers (spells can accomplish this, no need for a "species" to have this ability...any instances of dopplegangers are chalked up to evil magic users)
Driders (no one other than some troubled child has ever imagined something like this)
Ettin (once drawn in a childrens drawing, and just like other animals in nature a two-headed critter can be born, but especially in giant communities it would be eliminated shortly after birth. )
Gbolls (See animorphic above)
Gorgon (Singular magical constriction, there may be one out there guarding a maze somewhere...but it is not a "species" )
Hippogriff (We have/had Gryphons ... Hippogriff anatomy makes no sense)
Medusa (Singular cursed person, there may be one out there guarding a treasure somewhere...but it is not a "species" nor are there any stories of its existance)
Minotaurs (see above animorphic)
Rakshasa (see above animorphic)
Tarrasque (No lore exists regarding this creature)
Dinosaurs (No lore exists regarding any dinosaurs)
Werebear/rat/boar ETC (Werewolves exist in lore, however these other critters are just imagination)...see above animorphic