The Beyonder - at least in his pre-retcon form (his original history was ignored and he suddenly became a lot less powerful than he once was) - was an incredibly powerful character. What makes him different to most is that, generally, characters of his power level are neutral characters and for the most part so is he and they keep out of the every day lives of the characters we classically think of as superheroes and villains, but there have been times when the Beyonder has been outright villainous and, at those points, he has posed a threat to the entire Marvel universe just because he could. He initiated the original Secret Wars plot an arc in which he summons a group of both superheroes and supervillains and teleports them, against their will, to Battleworld a planet he created himself in a distant galaxy for them to fight on. He was virtually omnipotent, omnipresence and omniscience and he could warp they very reality around him. He could destroy galaxies and possessed vast psionic abilities that allowed him to control and manipulate matter and energy on a universal scale. In fact, he was shown to repel the planet-devouring Galactus "like a bug" and would have been even higher on this list prior to his decrease in power (maybe fourth or fifth).
10. Entropy
Entropy is the offspring of Eternity and considered himself to be his equal opposite - though that level of multiversal power has yet to be shown in his default form. That said, Entropy is still incredibly powerful. His purpose is simply to destroy, and he originally set out to destroy the universe and his father, and just being in the presence of Captain Marvel (the first mere mortal to lay eyes on him) made Marvel's cosmic awareness go out of control, which literally ended up driving him insane. In his quest to destroy his father and the universe, Entropy sought out Genis-Vell to help, as he didn't possess the power to do it alone. Together they managed to kill Eternity, but it caused a paradox that resulted in Entropy becoming a new version of Eternity. He then created a new universe to rectify the issue, but it wasn't perfect. As the conceptual embodiment of entropy itself, Entropy has a near unlimited ability to manipulate space, time, energy and matter on a cosmic scale.
