As long as Kabutops is your Active Pokémon, your opponent can't play any Basic Pokémon or Evolution cards from his or her hand to evolve his or her Active Pokémon.
Before doing damage, you may choose 1 of your opponent's Benched Pokémon and switch it with 1 of the Defending Pokémon. If you do, this attack does 20 damage to the new Defending Pokémon. Your opponent chooses the Defending Pokémon to switch.
