I must admit, I'm not at all experienced with competitive battling. Given that, I'd like to know what people think of this Butterfree:
Timid Butterfree w/ Focus Sash
252 Sp Att, 252 Spd, 6 HP
Sleep Powder
Toxic
Bug Buzz
Dream Eater
The idea is that you sleep powder the first pokemon, with the Focus Sash saving Butterfree from being killed on that first turn. Then, depending on the situation, you Dream Eater the pokemon, or you Toxic on the switch... unless you expect the next pokemon out to be immune to Toxic, either through Immunity, Poison Heal, or being Poison or Steel types, in which case you Bug Buzz to do a bit of damage. Then, unless you used Dream Eater successfully, you switch. Dream Eater, of course, is what you use if the opponent has only one pokemon remaining, or there is some other reason to expect them not to switch.
I picture this butterfree teamed up with a baton-passer that can boost Special Attack, or perhaps with Umbreon (Fake Tears, Wish, Baton Pass, Dark Pulse, with low Speed, or something similar).
But as I said, I have no experience with competitive battling. Is there any major hole in my idea that can't really be patched with suitable choices of other pokemon for the team?