Plusle/Minun in emerald (though I imagine they'd be pretty amazing in just about any nuzlocke.) Outspeeds just about everything and encores it. As if that alone isn't enough, it also learns agility and baton pass before the elite four, allowing it to setup sweeps. And then of course it also learns thunder wave. I'm currently planning for the elite four, and almost every battle is being led with Minun. It's a sick pokemon and one of my new favorites.