Mew @ Leftovers
Trait: Synchronize
EVs: 108 HP / 252 SAtk / 148 Spd
Timid Nature (+Spd, -Atk)
- Nasty Plot
- Psychic
- Fire Blast
- Baton Pass
This Mew is a fantastic team-player. It is very self-sufficient, able to roll over weakened teams with its strong STAB Psychic, and it covers steels well with Fire Blast. Fire Blast is chosen over Aura Sphere so that Scizor, Ferrothorn, Jirachi, and all of the other strong steel options can't set up in front of Mew. In fact, without Aura Sphere, you're really only losing the ability to beat Tyranitar and Heatran. The key here is to use Mew as a strong offensive presence while still maintaining significant momentum should you need to switch out through Baton Pass.
The EVs are selected carefully--the speed and nature allow Mew to out-speed any neutral-natured base 100, meaning that we force the enemy to choose quick Pokemon over strong Pokemon from the get-go. 252 EVs are put to SAtk so that Mew can cause as much damage as possible on its own, and then the rest of the EVs go into HP for overall bulk. The given EVs also give Mew a perfect Leftovers number, on top of that.
So, why Mew? Well, it's pretty simple. It's not weak against Stealth Rock, which is huge here. It can fair decently against any leads to its fair speed, fair bulk, ability to hit hard with pretty good coverage, and immediately threatens Baton Pass. It can escape any Pursuit, meaning that it isn't afraid of Tyranitar without Aura Sphere. It bounces back status thanks to Synchronize, and is quick enough to avoid most Taunts. Also, it opens Team 1 up to endless possibilities of teammates. Tons of Pokemon resist Bug, Dark, and Ghost, meaning that there are plenty of compatible teammates to throw Nasty Plot, too. Most phazers--except for the Lati-twins--can't really afford to fight against Mew. Also, with Fire Blast and Psychic, you can threaten the majority of the metagame at +2. You certainly need not worry about Spikes on the other team, as Roserade, Ferrothorn, and Skarmory are all swiftly dealt with.
In general, Mew can stand toe-to-toe with most of the metagame and either land KOs or pass to other teammates, allowing Team 1 to immediately scout the play of Team 2.
I've used this set to great success. The possibilities of Pokemon to pass Nasty Plot to that otherwise normally don't think about such boosts is endless--Keldeo, Landorus, Jolteon, Raikou, Suicune, Starmie, Latios, Gengar, Alakazam...
Mew stands well against offense with its bulk, defense with its boosting pressure and ability to maintain momentum, hazards with its coverage, taunt with its speed, and status with its ability. It is not to be underestimated.