Okay, this one won't work unless your opponent has a weak lead, but if it does work, well, you will have one ticked-off opponent on your hands.
Okay, so this is primarily a lead but can be used later as well:
Smeargle (M) @ Leftovers
Trait: Own Tempo
EVs: 252 HP / 4 Def / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Belly Drum/Swords Dance
- Baton Pass
First, go for either Agility or Belly Drum (use Belly Drum ONLY if your opponent's Pokemon can't one-hit the smeargle). If you use Belly Drum, follow up with Protect to regain some of the lost HP with Leftovers. After that, use Baton Pass to give the boost to either a speedy poke or a physical poke.
Used correctly, this can make any physical attacker with decent speed impossible to touch.
It should be taken note of that it would help lots to also have a priority attack on whoever you are Baton Passing to, because if you pass to, say, Salamence, an Ice Shard might almost kill it. So be aware.