Spoilers in white text, don't highlight if you don't wanna be spoiled on certain things. Please don't quote either.
Kefka (Destroys the damn world)
Ghirahim (Breaks apart giant boulders with his sword, catches your sword in between his fingers, etc)
Xenoblade character (Zanza, the evil god. He's a god. Need I say more?)
Last Story character (Jirall, the prince. Is a pussy at first, but when he goes crazy, he's freaking badass)
Probably more that I either don't know about or not coming to mind.