Giygas from Earthbound.
He is all-powerful, able to transcend Time and Space and destroy the universe, with total control over darkness and evil. His influence corrupts people and warp things. His power shattered his mind, making him totally irrational, unable to speak or even think coherently, so much that he needs the Devil's Machine to maintain a semblant of sapience. His nightmarish true form is inconceivable for a human mind and his very existence is beyond rationalization. 