Well XANA normally wouldn't be a huge deal, but there's a mech in play, so it'll probably possess that and buff it to the extreme. With edward at the wheel, he can modify it with his alchemy, bringing finer control to it, better weaponry, and he can mend any damage to the hull as it happens.
Against a poorly drawn lady gaga? I'd say it's a tie as they would atomize her then with the leftover force (there's a lot of leftover force) those atoms will be split and edward and the mech both are evaporated, leaving XANA as the sole victor. Smug AI bastard.