Kuinta

I would have to say Pain just because of his weird technique that looks like various counterparts of himself and also that he trained with Jiraiya and has a special eye technique that goes beyond the limits and abilities of both the byakugan and sharingan. He's also someone who mastered all elements for jutsus at a very early age not to mention that he's the leader of Akatsuki and kills Jiraiya. There's Konan as well, but all I have seen so far that she can do is her origami jutsu.