In a situation in which each character's respective dimension merges with the other, thus enhancing both with their "home power".
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-Sig by BlackZero30x-
Wow, unreal...My gosh.This is Amazing!I feel INCREDIBLE!!! Yes! Yes! Yes! Yes! I can win!I feel great!I CAN DO THIS!!!Yes!I'm home!I'm alive!This is all a miracle!I'm awake!I'm WIDE AWAKE!!! - Piccolo
I'm gonna say Dormammu too. There was an issue of Thor which had Odin and Dormammu going at it, but to Thor it looked like a chess game because his mind couldn't understand what was going on.
Long story short it turned out to be a draw. Anyone that can fight Odin to a draw in Asgard stomps Mephisto period.
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..even the outer hells are indifferent matters for they bow only to potent and archaic Nodens.