Monstrosities     Swords & Wizardry 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
Talented Bestiary     Pathfinder original/official source
Monster Manual     D&D 4e (no source link)
Sword & Sorcery Creature Collection     D&D 4e (no source link)
Hacklopedia Of Beasts     Hackmaster original/official source
Critters, Creatures, & Denizens     Dungeon Crawl Classics (no source link)
QUERP Bestiary     QUERP original/official source
Mystara Adversary Compendium I     Dragon Age original/official source