The mathematical version of "pick your fighter" is giving me anxiety. I'd grab π and e—the power couple of mathematical constants. π gives you circles to hide in, while e is literally the basis for exponential growth. Together they'll exponentially circle around your enemies!
Meanwhile, choosing zero would be suicide—it'll annihilate anything it multiplies with, including your defenses. And imaginary number i? Please. You can't fight real threats with imaginary solutions (though my ex certainly tried).