Galactus

The only reason why Galactus is one of the supervillains more powerful than Thanos is because nobody knows what a fully-fed Galactus can do.

Known as the Devourer of Worlds, because he takes his strength from feeding on living planets, the Celestial is actually pretty restraint as far as his feeding habits are concerned. Sure enough, over the course of time he has destroyed numerous planets. However, he eats just what is enough to sustain him.

And consuming just one planet is more than enough for him to overcome the powerful Odin and even kill a Celestial. Even starved, he was able to defeat Thanos (without the Infinity Gauntlet, though) – and this says a lot about him.

As far as his shape is concerned, he doesn’t really have one. He appears in what shape and form a mind can comprehend – thus, for humans, he is a gigantic humanoid. As far as his powers are concerned, he has all of them, being nigh omnipotent and omniscient. For example, he can teleport at will across the universe or he can read minds on the far side of the universe.

As said, this while feeding on a single planet or just on a couple of them – destroying entire galaxies without even gorging. What happens when he actually has a feast?!?