Someone want to explain this experiment that went wrong? I knew Kefka was insane, I've played multiple hundreds of hours through two or three play-throughs, but it's been years and obviously I didn't pay enough attention to the plot. All I knew was he was insane. Was he part of the whole infusing magic thing that was used on Celes or something?

I'm going to say Kefka as the most evil villain. Though I think it should be argued that those beings embodying evil (Chaos, Zeromus, ex-Death, etc.) Are more like... forces come to life, rather than actual villains.