Giovanni's Gyarados G2 5

Flip 2 coins. If both of them are heads, this attack does 20 damage to each other Pokémon (even your own). Don't apply Weakness and Resistance for this attack.

Unless this attack Knocks Out the Defending Pokémon, choose 1 of your opponent's Benched Pokémon and switch it with the Defending Pokémon.