“The illithid, or mind flayer, is an evil and feared creature of the Underdark; its powers are formidable and it feeds on the brains of any creature it encounters. Using arcane powers, it enslaves or destroys its foes, which include such powerful creatures as drow and kuo-toa.
Mind Flayers stand about 6 feet tall and have hideous mauve skin that glistens with slime. The head resembles an octopus, with white eyes (no pupils are evident) and four tentacles around its mouth, a round, many-toothed orifice like that of a lamprey. The creature has three reddish fingers and a thumb on each hand.
Illithids have infravision. They can communicate with any creatures via innate telepathy; they have no spoken language, although they often accompany their thoughts with hissing, and the eager lashing of their tentacles. Mind flayers dress in flowing robes, often with high, stiff collars, adorned with symbols of death and despair.” The Monstrous Manual, 2nd Edition