Skull Zombie
Sprites from Avactor by Eradrop
Moves and reacts slightly faster, and instead of firing a single shot it fires a burst of three weaker ones, but it's still easily dispatched and handy for replenishing your ammo.
Skull Shotgunner
Sprites by SpacemanStrife based on Eradrop's skull zombie
Moves and reacts slightly faster, but it's still easily dispatched and a premiere source of shotguns.
Skull Chaingunner
Sprites by SpacemanStrife, rolling head sprites recolored from Hell's Fury head by Vader
No changes in functionality. Having to fight them a second time is punishment enough.
Skeleton Imp
Sprites by SpacemanStrife
Moves slightly faster and throws up to four fireballs continuously when it attacks. Even a single skeleton imp can apply the same pressure as a group of regular imps, so they can’t be ignored as safely in close encounters. It has 15% less health, so they’ll fall more reliably to shotgun blasts at longer ranges.
Skeleton Demon
Sprites by SpacemanStrife
Randomly alternates between normal and fast walking speed, making it harder to hit accurately with projectile weapons at long range. They're still no match for Super Shotgun blasts.
Ghost Spectre
Modified Blood Fiend sprites (original by Eriance/Amuscaria)
Although it's more visible than the standard Spectre, it will project illusions that look and behave identically to itself to try and throw you off. It's still fairly easy to hit the real one, but you may second guess yourself and waste ammo if you're not paying attention.
Dragon Soul
Modified Burning Soul sprites (original by ???)
Its primary attack is to breathe fire at close range. It still has a charge attack, but it's a slower non-damaging move used to approach its target. This makes individuals less annoying to deal with than the Lost Soul, but beware of Dragon Soul swarms - they harmlessly pass through each other instead of infighting and will quickly pin you into a corner if not dealt with.
NOTE: Due to the fact they don't leave corpses behind to respawn, Dragon Souls always replace Lost Souls regardless of difficulty.
Slayer Knight
Uses shoulder pads from Hell-Forged's Draugr by Eriance/Amuscaria, all other edits by SpacemanStrife
Trading in the brute force of the Hell Knight for raw speed, this armored beast will try to rush in and dice you with its sword. Although it prefers melee, it can sling projectiles that are weak at close range but gain strength and speed equivalent to a Baron fireball after traveling in the air for a certain distance (thus maps that use Hell Knights as snipers will not suffer for their presence).
NOTE: When using LegenDoom, Slayer Knights enter a unique state upon turning legendary in which their movement speed is doubled and they fire projectiles at a fixed rate, so if you were hoping for them to stand in place and spam their weak projectile attack, you'll be in for quite a surprise. Stay vigilant!
Balrog
Combines graphics from Espi and Ebola's Afrit and Vader's Bruiser Demon
Throws two fireballs continuously when it attacks, followed by a spread of three. The real threat, however, is with its hellfire, which it will pass to any non-ghost monster within a certain range; Monsters with hellfire do not turn on each other and will not flinch from damage as long as the Balrog is alive. (They can still damage each other, fortunately, so you're still able to rely on infight damage on maps where it's encouraged, although it will be harder to accomplish.) Luckily, Balrogs don't leave corpses, so they cannot be resurrected.
Caco Lich
Sprites from Vader, edited by SpacemanStrife
More frail than its living counterpart, but it's more aggressive and follows up its projectile attack by breathing fire that inflicts rapid damage. Fighting them at close range is more dangerous now, although if you goad them into attacking other monsters, the fire can easily stunlock them.
Painbringer
Sprites by SpacemanStrife using edited graphics from hidfan's 2x neural upscale project
Instead of Lost Souls, the Painbringer shoots Hot Heads at a more frequent rate. They explode into three Dragon Souls on death.
NOTE: Due to the fact that they don't leave corpses behind to respawn, Painbringers will always replace Pain Elementals regardless of difficulty.
Hot Head
Sprites by SpacemanStrife
A Lost Soul variant that is much more fragile, but it explodes for moderate damage on contact with its target. Their presence along with their distinctive scream makes it easy to tell when there's a Painbringer that still needs to be dealt with. "If it's a Dragon Soul, you're good to go - If there's Hot Heads around you're in Painbringer Town!"
Phantom Revenant
Projectile sprites from Avactor by Eradrop, soul form uses modified Melee Revenant sprites by 00_Zombie_00
It has slightly less health, but it fires up to two projectiles in a row when attacking, one straight and one homing, although the order they're fired in is random. Once killed, its soul leaves its body and tries to punch you to death. The soul disappears if the main body is resurrected by an Archvile or Reaper. You can also stand on top of a Phantom Revenant while it's dying to prevent its soul from escaping.
Abhorrent
Sprites by SpacemanStrife
An aggressive variant of the Mancubus that moves incredibly fast when its target is not in its line of sight. This can be either a blessing or a curse depending on the map layout and your weapon set, so its health remains roughly the same.
Arachnobone
Sprites by SpacemanStrife
No changes in functionality.
Reaper
Sprites by SpacemanStrife, Lost Soul attack uses edited sprites from hidfan's 2x neural upscale project
Whenever it attacks, it performs one of four different actions based on its current situation: Uses the standard Archvile flame attack, summons a giant Lost Soul that homes in on its target, turns itself invisible until its next attack, or instantly gibs all zombies and imps surrounding it and creates Blood Skulls from their remains. The Blood Skull ritual takes priority if affected monsters are within range.
NOTE: The specific monsters that are affected by the Blood Skull ritual are the Former Human, Shotgunner, Chaingunner, Imp, and any monster that inherits from them.
Blood Skull
Realm667 monster by Gothic
Only appears when a Reaper gibs a zombie or imp. It floats slowly in the air while spitting boiling blood at its target. They’re more durable than the monsters they’re created from, so take care not to underestimate them.
Conqueror
Main sprites by SpacemanStrife, Guardian Cube and projectile sprites by Eriance/Amuscaria
Although it has 30% less health than the standard Mastermind, it has new defensive capabilities to help it handle the unfavorable positions it is placed in during the original Doom and Doom 2 campaigns. The three cubes orbiting its body can absorb damage and shoot fireballs, and they will continue to attack you even if the monster starts infighting. Its standard attack is a rapid-fire railgun. When it takes enough damage, it will start locking onto its target with an Archvile-esque countdown timer that explodes after 3 seconds regardless of whether or not it has line of sight; Hiding behind thin pillars is not enough to avoid this so you'll have to take cover behind a wall instead.
NOTE: Conquerors will always replace Spider Masterminds regardless of difficulty. This means that they only need to be fought once on Double Death.
Cyberdemon
No changes in functionality or appearance. (For now...) This means that they only need to be fought once on Double Death.
