|Mind Flayer (Illithid) - one of the most dangerous creatures in Dungeons & Dragons|
fantasy role playing game, Forgotten Realms version by Helmuttt
In the Dungeons & Dragons Fantasy Roleplaying Game (D&D) , illithids (commonly known as mind flayers) are monstrous humanoid aberrations with psionic powers. In a typical Dungeons & Dragons campaign setting, they live in the moist caverns and cities of the enormous Underdark. Illithids believe themselves to be the dominant species of the multiverse and use other intelligent creatures as thralls, slaves, and chattel.
Illithids have a basically humanoid body, but their head is octopus-like. They have four tentacles around a lamprey-like mouth, and require the brains of sentient creatures as part of their diet. An illithid who snares a living creature in all four of its tentacles can extract and devour its living brain. Their eyes are pale white, and they can see perfectly well in both darkness and light. Their sense of hearing is slightly poorer than a human's; they have difficulty distinguishing between several sounds mixed together. Their skin is purplish blue to gray-green and covered in mucus, and is very sensitive to sunlight. Though sunlight does not actually harm them, they loathe it with incredible ferocity.
One of the most feared powers is the dreaded Mind Blast, where the illithid emits a cone-shaped psionic shockwave with its mind in order to incapacitate any creature for a short amount of time. Illithids also have other psionic powers, generally telepathic in nature, although their exact effects have varied over editions. Other powers include a defensive psionic shield and powers of psionic domination for controlling the minds of others. More about Illithids on wikipedia
You can find Lords of Madness: The Book of Aberrations (Dungeons & Dragons d20 3.5 Fantasy Roleplaying Supplement) on Amazon with plenty of informations on this and other aberrations.