Monster Miscellany

The archvile and pain elemental's peculiar abilities make them among my favorite monsters. I wish the bestiary had more monsters like that.

Here are a few of my ideas. Feel free to create your own.

Guardian

Appearance: Looks somewhat like an archvile, but is shorter and shrouded in black flames and frozen in a pose of meditation. Has a fancy hat.
HP: 300.
Attack: Is completely stationary and does no damage on its own, but emanates an 1024-mu aura in every direction. Monsters within this aura take half damage from the player's weapons.
Strategic implications: The player should get rid of guardians early on in the battle, so as not to waste ammo, but this might not always be feasible.

Seismodemon

Appearance: Looks like a shorter, thinner cyberdemon, perhaps feminine.
HP: 500.
Attack: Stomps the ground and sends out a visible shock wave that travels outwards at a moderate speed in every direction up to 2048 map units and does distance-proportionate damage (something like 100 up close and 20 at maximum range). The wave is interrupted by obstacles such as pillars, making it sort of like an archvile. The attack can't traverse large distances in floor height (whatever turns out to be optimal). Similar to an archvile, it can't provoke infighting and won't target the player beyond a specified distance.
Strategic implications: Another monster that is threatening in small numbers in open spaces.

Baron of Heck

Appearance: A baron's torso with long red horizontal wings like a bat's, a large gaping mouth in the middle of its chest, eyes where the nipples should be. No head.
HP: 150.
Attack: Functions as a slow homing lost soul (i.e., slightly faster than SR-40), with a fast bite attack that does 5x8 damage when it gets within melee range. Chases the player relentlessly, even behind cover. Momentarily stalled when its pain chance is triggered.
Strategic implications: Should be killed.

Anathema

Inspiration: The Thing & DeadSpace
Think: a grotesque barely formed creature just like The Thing that has slight appearance changes as it consumes the dead.

A demented creature that can gradually become a greater threat as it consumes. When it devours the remains of the deceased, it acquires some of its organs and power with it. From an Imp arm that can throw fire balls to a CyderDemon's rocket launcher. This creature can evolve multiple times but only progresses to creatures more powerful than its current form. For example, it if has a Mancubus launcher it won't consume a pinky's legs and jaw.

HP: initially 150 - depending on creature consumed, up to 800
Attack: A bite but gains the ability of consumed monster
Strategic Implications Initially weak and slow but often should be a priority kill, especially when sharing rooms with other powerful demons.

IceVile

Appearance: A blue, frozen, emaciated corpse turned horned demon
HP: 1000
Attack: Standard Arch-vile attack is turned into a support unit; predictably, it freezes the player in place for a short duration, opening them up to the attacks of any nearby monsters. Also has a flurry of medium damage snowballs (4d8) to suppress the player.
Strategic implications: Placing him among a horde of other hellspawn make staying in the open a very dangerous choice. Getting frozen in place can kill the player quickly should other monsters throw enough damage at you. Staying in cover and luring the IceVile in close can ease killing him, although, any dead demons in between will be revived and ready to fight again.

...And because I was bored: Download
(For ZDoom, duh)

https://www.doomworld.com/vb/doom-general/66759-if-you-worked-at-id-and-where-in-charge-of-making-a-new-monster-what-would-it-be/

My post: https://www.doomworld.com/vb/post/1227574

Ass Soul

A variant of the lost soul that during its charge attack, resurrects any monster corpse it crosses in its path, paving a line of newly resurrected whenever crossing a pile of corpses.