The Monsters Know What They're Doing     Dungeons And Dragons original/official source
Angry Golem (web)     D&D 5e original/official source
Atlas Animalia     Any 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
Exotic Encounters     Pathfinder original/official source
Mythic Adventures     Pathfinder original/official source
Monster Manual     D&D 5e original/official source
Flee, Mortals     D&D 5e (no source link)
Monster Monday (web)     D&D 5e original/official source
Monster Ecology Anthology     D&D 5e (no source link)
Monster Manual     D&D 4e (no source link)
MojoBob (web)     D&D 2e original/official source
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
Critters, Creatures, & Denizens     Dungeon Crawl Classics (no source link)
Monsters Compendium     Heroes Of Adventure (no source link)
Manual Of Monsters     World Of Warcraft RPG original/official source
Godforsaken     Cypher System (no source link)
QUERP Bestiary     QUERP original/official source
Mystara Adversary Compendium I     Dragon Age original/official source
Creatures Of Barsaive     Earthdawn original/official source
Lairs And Encounters     Adventurer, Conqueror, King (no source link)
Baby Bestiary 1     Any original/official source