My fave villain of all time is Magneto. I like Darkseid's omega beams, and the fact that he rules an entire world. Electro's powers are basic but usable. Moonstone's intangibility would help for sure.
So if I combine all these villains powers and give them the authority over an entire planet, you have a really powerful villain. The likes of which could likely solo a lot of teams.
Big Bad: His name.
Powers: Magneto's (all of them, even the ridiculous wormhole one) Electro's, Moonstone's, and Darkseid's post-crisis.
So what do you guys think? Could he solo the avengers? Maybe the JLA? I know he could solo the Fantasic 4. And Batman could prep all he wants, he bites the dust with this guy.