If I were you I would make it mostly physical. Surf hits... what? Not providing much, I'd say. Replace it for ExtremeSpeed for priority. Thunderbolt should be replaced for Thunder to counter Kyogre. Turn the EVs into 252 Atk/140 Sp. Atk/166 Spd
Make it your lead. Explosion won't be doing much, will it? I always use Occa Berry to stop all those nowadays anti-Ferro and Forretress counters. And replace Stealth Rock for Toxic Spikes, it helps a lot more in my experience.
Try for a sweeper. Nature should be Timid. And why would you increase Atk when you're using all special moves anyway? EVs are standard special sweeper 252 Sp. Atk/252 Spd/4 HP
Nice wallbreaker. All I have to say is no SR, there are plenty of alternatives ;D I'd recommend Torment, as most walls don't have more than one attacking move.
RestTalk Cresselia? Don't get stuck with Psycho Shift... Try a stalling Cresselia.
Cresselia @ Leftovers
EVs: 252 HP/128 Def/128 Sp. Defense
Moves: Toxic, Psychic, Protect, Calm Mind
Overall, a cool team. Mew's stats are sort of mediocre, but I try to keep all the askers Pokemon when RMTing. I hope you like my suggestions!