Butterfree is UU and Bug/Flying Type. Not much else to say, Butterfree really sucks.

Tailwind
Item:FocusSash
Moves:TailWind/ShadowBall/BugBuzz/HP Water or Ice
Nature: Modest
Ev's: 252 Spec.Atk/252 Speed

Really just some team support, tailwind up and sash, then do what damage you can. Also a good opportunity for a switch.

Counters: Almost everysingle pokemon in the game.

ChoiceSpecs
Item:ChoiceSpecs
Moves:BugBuzz/ShadowBall/Psychic/HP Water or Ice
Nature:Timid/Modest
Ev's: 252 Spec.Atk/252 Speed

Butterfree has decent speed, but its "just below mediocre" special attack score makes it NU. With Choice Specs, it can deal some damage tho. It is reccamend to pass some speed from a ninjask or something first, so Butterfree is espcially nice in BP Teams. Run Modest is an Agility or 2+ Speed Boosts are being passed.

Counters: Anything capable of taking its hits will pretty much own it, Alakazam with a sash can take the hit, and then KO with a STAB or SE Move ( Psychic or ChargeBeam or HP Ice )

Special Wall
Item:Leftovers
Moves:SleepPowder/DreamEater/BugBuzz/SafeGuard
Nature:Calm
Ev's:252 Spec.Def/252 HitPoints

Butterfree maintains a decent special defense score. Its Dream Eater ability only makes it much more scary, and this set actually doesnt suck so bad. Sadly, its Special Defenses arent enough to survive a Power Gem from a good special attacker or FireBlast from a LO Mence.

Counters: Basically, any physical attack or high power SE special attack can OHKO or do well above 50%, forcing you to rely on Sleep Powders imperfect accuracy to recover back to good hp.