I think you just have to make sure that enemies are being killed within range. Your Metapod can just sit there and harden while other Pokemon deal the damage. At least, I think that's how I did it with both Metapod and Kakuna
played this last night, and subsequently dreamed up a first person HD graphix pokemans game, all I remember is shooting something inside a Venousaur's mouth and it trying to take me out before it was knocked out sounds like a porno imo