Gargoyle

The Monsters Know What They're Doing     Dungeons And Dragons original/official source

Angry Golem (web)     D&D 5e original/official source

OSE Encounter Activity Tables     Any original/official source

Pathfinder 1e Bestiary 1     Pathfinder original/official source

Pathfinder 2e Bestiary 1     Pathfinder original/official source

Tome Of Horrors Complete     Pathfinder original/official source

Classic Horrors Revisited     Pathfinder original/official source

Exotic Encounters     Pathfinder original/official source

Mythic Adventures     Pathfinder original/official source

Monster Manual     D&D 5e original/official source

Monster Monday (web)     D&D 5e original/official source

Monsters Of The Underworld     D&D 5e original/official source

Monster Ecology Anthology     D&D 5e (no source link)

Monster Manual     D&D 4e (no source link)

Monster Manual 3     D&D 4e (no source link)

Dungeons And Dragons Essentials: Monster Vault     D&D 4e (no source link)

D&D 2e Monstrous Manual     D&D 2e (no source link)

Scruffy Grognard's Monstrous Manual     D&D 2e (no source link)

AD&D Monster Manual     AD&D 1e (no source link)

Dragonlance Bestiary     SAGA (no source link)

Hacklopedia Of Beasts     Hackmaster original/official source

Monster Guide     World Of Warcraft RPG original/official source

Fantasy Age Bestiary     Fantasy Age original/official source

Iron Falcon Handbook Of Monsters     OSR (no source link)

Lairs And Encounters     Adventurer, Conqueror, King (no source link)

Baby Bestiary 2     Any original/official source