Rae
"Yeah, well see, "Terry" is intelligent and pragmatic, but he's rather short sighted. He has a small bit of empathy and gross stuff like that. I on the other hand crave power, and if get to eat "Thomas" I'll be more powerful than ever."
"This comes with the nice caveat of saving the world at the same time!"
"I see. Thank you for your honesty," I coolly reply, "We cannot come to an agreement. For empathy and the like are very much important. Farewell."
With the fight having begun, it is time to do my part. Why yes, I'm quite angry at the brazenness and power-lust of this Terry, but it's with a tranquil face, and an aura of roiling darkness.
Using my array of powers, I make my attack from multiple fronts. Physically, my black Keyblade materializes in a flash of shadow as I twirl it around me, manipulating the oncoming water with magic to whip at the villain, again and again.
Mentally, I telepathically assault his mind, intending to mislead him via manipulating his perception. Where he'd think we are, we simply aren't. At the same time, illusory attacks would help disguise the real ones or provide openings for them.
Lastly, biologically, my empowered mitochondria get to work as they attempt to seize command of his cells, to make them set him on fire via producing excessive heat. Failing that, his cells would instead be commanded to multiply endlessly and haphazardly, not much different from tumors or cancer.