Accuracy Control is key here. A Coleoseum is a fairly open battlefield. However in the Coleoseum of Forbidden Illusions, it's hard to even know where your opponent is. Luis_Sera89 can close his eyes and use Accuracy Control to fling whatever attacks he wants at Some_Character. Illusions in a Coleoseum are likely to include a lot of fake attacks. Some_Character won't know which are real and will have to defend against a ton of fake ones. Once again with Accuracy Control, Luis_Sera89 can assume they won't connect.
Luis_Sera89 uses Accuracy Control + Greater Casting of the Thunderous Chain to take out Some_Character before Some_Character can track him down is how I see the battle going.
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SuperNiceDog was not so nice to my bracket.
Congrats to SuperNiceDog for winning the Rivalry Rumble Guru Contest!