Some "concept frames" I made for monster ideas when I was bored years back.
Possessed armor

- possessedarmor.png (12.63 KiB) Viewed 18746 times
Resistant to fire damage, prolonged charging attack like Quake's knight. Restricted in the numbers and level themes it could be used in, might make for a good mini-boss.
Blob

- jelly.png (18 KiB) Viewed 18746 times
Splits into smaller versions as it takes damage. Engulfs players, making them stuck in place as it deals damage, requiring rapid mashing of the use key to escape.
Werewolf

- wolf2.png (9.99 KiB) Viewed 18746 times
Very fast, hard-hitting. Functions on land much like a gill beast functions underwater. Can morph from civilians.
Wraith

- wraith.png (35.41 KiB) Viewed 18746 times
Thought of it as a classic style rendition of Blood 2's death shroud.
Acolyte replacement

- acolyte.png (7.68 KiB) Viewed 18746 times
Having so many cultist recolors running around cheapens the vibe. Would be a lot better if at least one of them had its own unique sprites.
Blood 2 zealot

- zealot.png (8.85 KiB) Viewed 18746 times
Would behave much like the Blood 2 wizard. Strong magic attack, close range shockwave and teleportation. Flare gun fodder.