Yeah, Protean Greninja is indeed awesome. Too bad the rumor that he had Rapid Spin is nothing but a lie; he would be an awesome lead. Sure, he does lack in defense, but its ability so unique, allowing him to always gain STAB and it's too hard to score a S-E hit on him AFTER he moves, as you're working with his current type or with what you think he'll use. Personally, I've used one with U-Turn, Spikes, Hydro Pump and Ice Beam. U-Turn is great for switching, and considering few would use a Fire or a Flying type move in a pokemon whose type is Water/Dark.
And don't forget of Klefki. That thing is great! He has a great typing, granting him several resistances and two immunities and a good ability in Prankster and a good movepool in support. The problem with him is his defenses and HP.
Also, Goodra in Rain is good and he has a quite good bulk and offensive stats, too bad weather was nerfed in X/Y.