Butterfree

Whirlwind

20

If your opponent has any Benched Pokémon, he or she chooses 1 of them and switches it with the Defending Pokémon. (Do the damage before switching the Pokémon.)

Mega Drain

40

Remove a number of damage counters from Butterfree equal to half the damage done to the Defending Pokémon (after applying Weakness and Resistance) (rounded up to the nearest 10).