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When Jonouchi's weird dreams first come into play in the Duelist Kingdom, he finds himself facing down the embodiment of the Millennium Eye as it hunts down the last piece of Seto Kaiba's soul, which took the form of Kaiba's younger self. His solution to escaping the thing? Jump through it's eye. And it worked.
Yugi managed to top this by destroying it from inside Yami Yugi's head by simply telling it to leave. Watching Eldritch Abominations die has never been so sweet.
And lets not forget Kaiba's own non-canonical moment during the Legendary Heroes arc, topped off with this line: 'I don't need cards to fight.' Realize that her arm was literally in flames as Kaiba was saying this, and that the line was followed by her cutting through a duel monster with that same arm.
Also from the Legendary Heroes arc, there's Mai, who took down three dragon heads in a few seconds during the final battle of the so-called game. That entire arc is filled with CMOA's when you look back.