OSE Encounter Activity Tables     Any original/official source
Pathfinder 2e Bestiary 1     Pathfinder original/official source
Tome Of Horrors Complete     Pathfinder original/official source
Kobold Press Tome Of Beasts 2     D&D 5e original/official source
Critters, Creatures, & Denizens     Dungeon Crawl Classics (no source link)