Marvel/DC vs. Earth
Who is the least powerful being in the DCU that could feasibly take over our planet? And who is the least powerful being in Marvel that could feasibly take over our planet? Assume that once said characters have breached over, no one in the comic industry could retcon or otherwise affect them through the industry. We can also not somehow "summon" another comic book character to defend ourselves.
Is essence, the characters become real and possess any powers, abilities, and skills they have in the comics. We, of course, would have any and all knowledge of them because they are fictional characters.
Just how screwed are we when they make their move?