Using it right now. a mixed evs support can make it sweep away teams.
Trait: Torrent --- Mega Launcher
Evs: 4hp, 208 atk, 28 def, 252 spa, 16 spd.
Nature: Quiet (+spa-spe)
Ice Beam (90 power, coverage against grass types, may freeze the opponent, pretty much always hits. every water type with a good sp.a. stat should have it ((if it learns)) )
Dragon Pulse (85 base power, pretty much always hits, boosted by mega launcher, takes care of most dragon types. also deals a great damage to any other damage which don't resist it).
Aura Sphere (80 Base power, booster by mega launcher, has to hit, covers 5 types. just awesome)
Aqua Tail (good to have a physical attack anyways, you also get a STAB boost. accuracy is not bad too.)
It's slow, but bulky enough to hung on a move. and if you do so, your opponent will be in some troubles.