I feel like Finn and Jake will be one of the most powerful duos in Learning With Pibby. Finn defeated the Lich which is basically death, and also Finn basically beaten the god of his universe, Glob. Jake also has stretchy powers which can make him big and even shrink him, also in one episode it is revealed that Jake can even enlarge his insides. Jake can also use his powers to transform into weapons, so he could possibly help other corrupted character's fight. (Which is pretty bad for Pibby)
Assuming Ben and Gwen get corrupted, it’d probably them imo. Ben contained the big bang and can turn into an immortal god who can recreate an entire universe, and the only thing holding Gwen back from nigh-omnipotence is the fact that she’d need to throw away her humanity, which probably isn’t an issue for corrupt Gwen. You could also make a case for Rick and Morty since Rick’s aware of the 4th wall and has destroyed at least two governments, several personifications of parts of reality and at least one universe, and Morty cleans up after him, has outsmarted him a fair few times and has pulled some insane stuff himself, but they both rely on their minds which their corrupt selves might not be able to fully use.
