7. The Mask (Dark Horse Comics)
I have a feeling this one might be controversial, but that doesn't change the fact that it's true! The Mask, although often portrayed as a bit of a joke character (particularly in the live action movie), is actually an insanely powerful character in the comic books. He is essentially a cartoon character, possessing "toonforce", which basically enables him to conjure any power as he pleases and warp the very reality around him. He has never displayed physical strength on a par with Superman - that's a given - but it's the fact that he has such crazy durability and unkillability (meaning there is literally nothing that Superman can do to permanently put him down) in addition to the fact that he could turn Superman in to a bar of chocolate if he wanted to that makes him more powerful than the man of steel. The Mask has been at ground zero of a blast that destroyed a solar system and survived unscathed (in fact, he found it funny). He has also been blasted in to tiny little bits - each of which simply became independent little versions of the character, operating on their own, before simply coming back together to reform the Mask back to normal. He has also simply no-sold magic transmutation - he was magically turned in to a lump of cheese, but simply turned himself back to normal using his powers. The Mask is no slouch when it comes to speed either - a Mask wearer conjured a motorbike for himself out of nowhere and proceeded to ride around the Earth multiple times in a single panel, so his powers can clearly spawn speed powers on a par with Superman (indeed, he actually turned himself in to a version of the Flash in one scene in order to outrun a bullet and catch it in his mouth). The Mask also demonstrates the ability to mind-control people in to doing things they don't want to do (for a mainstream version, think of the dance scene in the movie). I can picture him making Superman beat himself up. Basically, if the two fought, Superman could pummel the Mask in to tiny pieces, but the Mask would never, ever be permanently put down - and then he could just mind-control Superman or turn him in to something funny... like a piece of Kryptonite.