Thanos Vs. Onslaught
I saw the Thanos vs. marvel villains thread. I think it's a bit of an unfair fight given how ludicrously overpowered Thanos is. So I put him against the strongest Marvel villain I know and the only one outside of god-like beings like Galactus who could take Thanos solo and have a good shot of winning. And with Onslaught making a comeback in the wake of House of M, we might see this fight happen potentially.
Onslaught vs. Thanos. No prep, no warning beyond the usual villain speeh before fights. Fight takes place on earth. Thanos attempts to take over earth as in the marvel villains vs. him thread, but this time the destruction of the heroes has brought back Onslaught (I know that it was really the scarlet witch, but this is what if? anyway.) and he's pissed.
Good bye earth, hello planet Onslaught or planet thanos.