Anthropophagi, aka Shark Monkeys, are deadly and terrifying. They have no heads. Their eyes are on their shoulders, their mouths are on their stomachs (which are full of razor sharp teeth), and their brains are in their groin area because that's probably a subtle joke to the way most men think. They're also quite large (about 8 feet tall), and have long arms with razor-sharp claws on the end of them, which they use to pick meat out of each others teeth. How sweet! Also, I can neither prove nor disprove that they get together, put on monocles and top hats, and have tea parties.
Wendigos aren't supposed to exist so I will merely insert a song.
Rudolph the Canadian cannibal
Had a really rotten nose
And if you ever saw it
You would really say it's gross
All of the other natives
Always screamed and ran away
They never let poor Rudolph
Join in any festive games
Then one foggy winter night, Monstrumologists came
Pellinore screamed "YOU DON'T EXIST"
And poor Rudolph ran away
Then all the Natives were safe
So they shouted out with glee
But Pellinore the Monstrumologist
Never went down in history
Dammit I made myself sad
Mongolian Death Worms, aka Cuddle Worms, are exactly what they sound like: worms that live in the deserts of Mongolia. You might recognize them as an actual cryptid, to which I say GOOD FOR YOU. They surprisingly small, and have a deadly toxin they use to subdue and consume their prey. They're also hermaphrodites. IT IS ESSENTIAL THAT YOU REMEMBER THEY ARE HERMAPHRODITES!
And then there's the Sugar Bowl. You know, that bowl made out of flesh? It's part pwdr sêr (which is an actual thing), and part your worst nightmare. The creatures that make them are said to be the Holy Grail of Monstrumology, which doesn't make sense with Pellinore's name analogy because King Pellinore was after the Questing Beast. But then again those things are technically beasts so I guess it still counts? I have no idea and I can't say much more without spoiling book three. But yeah... SUGAR BOWLS.