Dude, I know it's not anime, but if you want a head trip from X-Men, Mojo's your guy. I can not watch the two episodes he's in. He's just so annoying and gross.
As for the nastiest bad guy in an anime, umm, I'd hae to say, Chin Yisou from Saiyuki. He was a dude that would trip with people's minds. Creepy as all hell.