The most insanely powerful villains in comics tend to have their power levels fluctuate the most wildly depending on who's writing them. Such is the case of the Beyonder. He was essentially a sentient universe, capable of doing absolutely anything in our universe with, as Captain America says, "such power that nothing in the universe can take place without his consent." The Beyonder started out as a remote game-master, then briefly lost his power to Doctor Doom in an impossible, million-to-one gambit that might've been Doom's finest hour. Regaining it after messing with Doom's head, the Beyonder went on a quest to understand humanity which ended, inevitably, with the conclusion that we were all assholes and must be destroyed. To some degree, the Beyonder was Jim Shooter's autobiography. He wrote both Secret Wars I and II when he was editor-in-chief of Marvel, so he was theoretically all-powerful but always frustrated, too. As soon as he left the company, the Beyonder started getting less and less powerful and interesting until he was basically an irritable kid alien psychic.