Monster

Doom/Ultimate Doom

 * Baron Of Hell
 * Cacodemon
 * Cyberdemon
 * Demon
 * Former Human
 * Former Human Sergeant
 * Imp
 * Lost Soul
 * Spectre
 * Spider Mastermind

Doom 2/Final Doom
All of the original Doom monsters, plus
 * Arachnotron
 * Archvile
 * Chaingunner
 * Commander Keen
 * Hell Knight
 * Icon Of Sin
 * Mancubus
 * Pain Elemental
 * Revenant
 * Wolfenstein SS

Heretic

 * Disciple Of D'Sparil
 * D'Sparil
 * Fire Gargoyle
 * Gargoyle
 * Golem
 * Golem Ghost
 * Iron Lich
 * Maulotaur
 * Nitrogolem
 * Nitrogolem Ghost
 * Ophidian
 * Sabreclaw
 * Undead Warrior
 * Undead Warrior Ghost
 * Weredragon