The Fiend Folio is a glorious compendium of weirdos and oddball monsters created by AD&D players and sent to a British magazine for their Fiend Folio feature, most never actually published in the magazine.
This particular Fiend Folio, however, was not just used, but improved. An enterprising former owner with a rainbow selection of markers had gone through the Tome and colored every picture in the book.
The dreaded Grell assaults some foolish adventurers who dared penetrate its lair.
The psionic Githyanki come forth from the Astral Plane, clad in bejeweled +4 Splint Mail and wielding intelligent Silver Swords of great power. Woe is the reward of any dungeon despoilers who stumble upon a Githyanki Prime Material Plane Lair, containing 21-30 of the rebel Mind Flayer creations.
Much care was given to rendering the Flail Snail's scintillating shell.
Even the Flumph received attention.
Pure white, save for the eyes. Tastes like that artificial 'crab' salad with too much mayo.
The Flumph "flies" by, well, farting. And attacks with a foul-smelling liquid which results in the victim being "shunned by his companions" for several hours until the scent passes. Also, our Flumph is helpless if turned over, and is the only creature of Good alignment in the entire tome.
Care was taken to vary the plumage of the individual Achaierai.
The Kenku, everybody's favorite "can I make a character of this race?" critter.
Sleepy Black Dragons. And Dragon Subtable for your random monster encounter episode. If you're randomly generating dragons, something has gone wrong with your campaign. Very wrong.
And some Lava Children battling the Lizard King. Based on a mumbling ramble by Jim Morrison at some where and when no one can recall. But does it matter where and when or what was said and who was saying? That's what my parole officer won't tell me.