Aboleth

The aboleth is a loathsome amphibious creature that lives in subterranean caves and lakes. It despises most land-dwelling creatures and seeks to enslave intelligent surface beings. It is as cruel as it is intelligent.

An aboleth resembles a plump fish, 20 feet in length from its bulbous head to its fluke-like tail. Its body is blue-green with gray splotches, and its pink-tan underbelly conceals a toothless, rubbery mouth. Three slit-like eyes, purple-red in color and protected by bony ridges, are set one atop the other in the front of its head. Four pulsating blue-black orifices line the bottom of its body and secrete gray slime that smells like rancid grease. Four leathery tentacles, each 10 feet in length, grow from its head. An aboleth uses its tail to propel itself through the water and its tentacles to drag itself along dry land.

Note: Aboleth originally appeared in this form in the 2nd Edition Monstrous Manual for the AD&D game from TSR. Their use here is for the purposes of providing context for the campaign only.