Monsters are entities in Doom that will attack you in many ways.

All monsters in The Ultimate Doom are:

  • Zombieman: uses a pistol to attack you.
  • Shotgun guy: another former human, uses the shotgun to attack you, and you may take damamge while battling with them.
  • Imp: a brownish monster that throws fireballs at you, or uses scratching as melee attack.
  • Demon: Pink, yellow-eyed monster that will keep coming towards you to bite you, and eventually eat you.
  • Spectre: same as the Demon, except that he got a partial invisibility artifact during the invasion from hell.
  • Baron of Hell: always appear in Thy Flesh Consumed, they throw green toxin balls to attack you, and, similar to the Imp, can use scratching as melee attack.
  • Cacodemon: green-eyed tomato that can fly, and will spit powerfull balls of plasma at you, and, similar to the Demon and Spectre, comes close to you to bite you, and eventually eat you, as a melee attack.
  • Lost soul: flying flaming skulls that will keep coming towards you to gore you. For some reason, killed lost souls are NOT included in the kills percentage at the end of each level.
  • Cyberdemom: acts as boss in The Shores of Hell, launches rockets at you until you die. One of the most powerfull monsters in Doom.
  • Spider Mastermind: acts as boss in Inferno and Thy Flesh Consumed, spider-shaped monster with an obvious brain, has a super chaingun (aka rapid shotgun) to kill you, and can kill you easily more than the Cyberdemon, since the shotgun is very powerfull, and making the shotgun rapid is more powerfull.

The higher the skill level, the more of these monsters are likely to appear in each mission.