Dracopedia Bestiary: An Artist's Guide     Any original/official source
The Monsters Know What They're Doing     Dungeons And Dragons original/official source
Pathfinder 1e Bestiary 1     Pathfinder original/official source
Pathfinder 2e Bestiary 1     Pathfinder original/official source
Pathfinder 2e Bestiary 2     Pathfinder original/official source
Monster Manual     D&D 5e original/official source
Monster Manual Expanded v3     D&D 5e original/official source
Asian Monsters     D&D 5e original/official source
Critter Compendium     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)
MojoBob (web)     D&D 2e original/official source
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)
Monster Guide     World Of Warcraft RPG original/official source
The Monster Overhaul     OSR (no source link)
Dungeon Fantasy Monsters 2     GURPS 4e original/official source
Baby Bestiary 2     Any original/official source