Ok, this one has been figured out on the Chat at 1:27 PM, 13th of July, 2012 by me and Trachy.
To note that this is a Double Battle strategy.
So you start with Mienshao and Whimsicott!
First, use Tailwind with Whimsicott.
With Mienshao, use the move that you want.
Next turn, both of them use U-Turn. Tailwind almost ensures them of moving first and thus leaving untouched.
Put in Seaking and Shedinja.
Make sure Seaking as LightningRod as his Ability.
With Shedinja, have this moveset:
Shedinja @ Focus Sash
Trait: Wonder Guard
EVs: 252 Atk/ 252 Spd
Adamant Nature (+Atk,-SAtk)
- Swords Dance
- Shadow Claw
- Sucker Punch
Note that this moveset is optional. Use the moveset you desire.
With Seaking, use Soak.
With Shedinja, use Swords Dance.
Now, Shedinja only has two weaknesses! Seaking and Shedinja's low Speed Stats are boosted by Tailwind. Shedinja's two weaknesses are Grass and Electric types. The Electric type is absorbed by Seaking and Grass types... well, switch into Whimsicott! Or don't. With Whimsicott's amazing Ability, Prankster, it is guaranteed that he can set Tailwind up before fainting. Though it's better if he doesn't faint. After using Swords Dance with Shedinja, you can use it again and again and then start sweeping. Grass-types are defeated by X-Scissor.