Thanos vs Earth
Thanos has come to earth with an device which has neutralized the mutant powers of every mutant on earth. He comes with Mangog and Terrax, and the Destroyer. Thanos has also sealed off Earth from any new opponents. Can the current denizens of Earth stop Thanos before he razes the whole planet? His mission is to capture and study Jean Grey. Does he get to disect Jean Grey. Assume that without her mutant powers, Jean can't tap into the Phoenix Force.
ummm... all of earth is extremely broad. regardless of the neutralized mutants there are still hundreds upon hundreds of other worthy heroes that would pose an extreme threat to this band of four. not saying they wouldn't pose a threat, because these four would be hell for earth to deal with unprepared. and even though im certain that thanos would have an amazing foolproof plan for his takeover, there is no way a writer could resist the temptation of making earth unite and destroy what otherwise would be a multiversal threat.
all in all i think it depends where this would happen... if it was like a thanos miniseries or some cosmic series, thanos and his band would take it and the whole story of earth's destruction and takeover would be summed up in like two pages.
if it was in the fantastic four or like the avengers or anything like that, it would probably be a long drawn out battle in which the heroes of earth finally defeat the massive threat.
i can see it going either way, but because i like thanos and i think he could pull it off, ill go witht the first scenario.