Spiritomb..
I mean, really.. look at it. D8
I've never had a Pokemon scare me before, or creep me out, looks-wise, but I think Spirtomb just might. It looks like the love child between the Flu virus, and a Gastley. The only Pokemon that's creeped me out though, wasn't for apperance really, but it was one of the Regi's in the Lucario movie. >.> The way it sounded really bugged me for some reason.. plus it does look kinda weird.