Deepspawn

Your classic “monster in the trash compactor” a la Star Wars. The creature is born in toxic waste or blights and thrives on refuse and disease; while created by unnatural means (magical runoff, a curse gone awry, blight), it becomes a part of the ruined environment as a wild animal. It uses objects it finds deposited in its lair as weapons by whipping them around with its tentacles (and is also fond of picking up victims and using them as weapons). The Deepspawn prefers to hides underneath sludge or dark pools and strike from stealth. It can peek out an eyestalk surreptitiously to spy on intruders and produce spell-like effects due to its mutant physiology, which are not spells unto themselves (and therefore cannot be countered). Swimming in its fetid pools causes disease.