My Seviper, because, back in Emerald times, I had gotten to Queen Lucy in the Frontier twice and was defeated twice. So the third time I got up to her, she sent out her Seviper first, of course. I had something out there [I think my Sceptile or something?] so I switched my Seviper out [this is such a noob story xP]. Anyway, she swaggered my Seviper. Next turn, I managed to not hurt myself and killed her snake with a one-hit-KO. She sends out her Milotic, and on the first turn, I survive a surf, snap out of confusion and kill it with critical hit Sludge Bomb or something. And it only took three EQ's to kill her Shuckle. Though it was all completely thanks to luck and Swagger, Seviper has since become my favorite Pokemon, and that particular ones has gone on to dominate in D/P.