Whirlwind20

Your opponent switches the Defending Pokemon with 1 of his or her Benched Pokemon, if any. (Do the damage before switching the Pokemon.)

Mega Drain40

Remove a number of damage counters from Butterfree equal of half the damage done to the Defending Pokemon (after applying Weakness and Resistance) (rounded up to the nearest 10). If Butterfree has fewer damage counters that that, remove all of them.