So many options, so little time. But I do have a question. Does the person you summon have to help you? Because if so, Wolverine. Sure, it's a slow process, but I'm not sure there's a weapon that can kill him, he beat the Hulk and I'm very patient.
If not, Wario. No seriously! He's easily bribed with, say, all the world's gold. He's none too bright so he won't usurp me, but thanks to cartoon physics nothing you do to him can even make him bleed! He's flattened, he reinflates. He's shot, so he fires into the air with a trail of smoke behind him. Eventually he wins, because he can punch through a brick wall and make rudimentary explosives out of nothing.
