If you could get yourself a Moxie Gyarados, that would be great. 8) For moveset, I would personally go with Dragon Dance, Earthquake, Waterfall, and Stone Edge. After one Dragon Dance, it could take down the entire team of whichever Elite Four member you're facing. Since all your slots are filled, maybe you could replace Swanna. Make sure to EV train it in Attack and Speed, by the way!