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
Monster Codex     Pathfinder original/official source
Classic Horrors Revisited     Pathfinder original/official source
All Sorts Of Critters (web)     Pathfinder original/official source
Monster Manual     D&D 5e original/official source
Book Of Beautiful Horrors     D&D 5e (no source link)
Old Gus: Plantfolk, Undead, And Other Oddities     D&D 5e original/official source
Monsters Of The Orient     D&D 5e (no source link)
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)
13th Age Bestiary     13th Age original/official source
Dragonlance Bestiary     SAGA (no source link)
Hacklopedia Of Beasts     Hackmaster original/official source
Critters, Creatures, & Denizens     Dungeon Crawl Classics (no source link)
Monster Guide     World Of Warcraft RPG original/official source
Old World Bestiary     Warhammer original/official source
Fantasy Age Bestiary     Fantasy Age original/official source
Mystara Adversary Compendium I     Dragon Age original/official source
Abnormal Undead     Any original/official source