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
 * Former Human Commando
 * 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

Hexen

 * Affrit
 * Brown Chaos Serpent
 * Centaur
 * Dark Bishop
 * Dragon Lich
 * Ettin
 * Green Chaos Serpent
 * Heresiarch
 * Korax
 * Maulotaur
 * Menelkir
 * Reiver
 * Slaughtar
 * Stalker
 * Stalker Boss
 * Traductus
 * Wendigo
 * Zedek

Enemies

 * Acolyte
 * Bishop
 * Ceiling Turret
 * Crusader
 * Entity
 * Entity Nest
 * Entity Pod
 * Inquisitor
 * Loremaster
 * Programmer
 * Reaver
 * Security Bot
 * Sentinel
 * Shadow Acolyte
 * Specters
 * Spidibot
 * Stalker
 * Templar

NPCs

 * Macil
 * Rebel
 * Peasants
 * Armorer
 * Bar Keep
 * Becoming Acolyte
 * Beggars
 * Kneeling Guy
 * Medic
 * Oracle
 * Weapon Smith
 * Zombie