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 1e Bestiary 2     Pathfinder original/official source
Tome Of Horrors Complete     Pathfinder original/official source
Fifth Edition Foes     D&D 5e original/official source
Tome Of Horrors 2018     D&D 5e original/official source
Creatures Of Vathis     D&D 5e original/official source
D&D 2e Monstrous Manual     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
Critters, Creatures, & Denizens     Dungeon Crawl Classics (no source link)
Monsters Compendium     Heroes Of Adventure (no source link)