If, somehow, Baton Pass and Guard Share aren't Illegal, I definitely see an decent set coming off this guy.
Agi@Focus Sash
Ability: Unburden
EVs: 252 Spe/252 SpAtk
Nature: Rash|Mild(+SpAtk/-Def|SpDef)
Moves:
~ Guard Share
~ Baton Pass/U-turn
~ Bug Buzz
~ HP Water
Come in, and Guard Share when you take a hit. Focus Sash keeps you alive, and their defenses are SEVERELY lowered. Next turn, IF they don't have priority, you can either try to take them out, or Baton Pass away. If I'm thinking correctly, then you'll pass the Unburden boost to the next poke, but if you can't do that, then U-turn is the better option. This way you can scout for a switch, and if they don't you can bring in something powerful to deal with their newly weakened Pokemon. Shadow Tag Shandera loves this, btw. Bug Buzz is obligatory STAB, and HP Water hits Fires/Steels/Rocks. Notably, Heatran, Shandera, and Doryuzuu. You'll have trouble with Gyarados though.