Once during your turn (before your attack), when you play Skuntank from your hand to evolve 1 of your Active Pokémon, you may choose 1 of the Defending Pokémon. If that Pokémon tries to attack during your opponent's next turn, that attack does nothing.
This card later received an erratum to change the Evolutionary Gas Poké-POWER by adding the text "(If the Defending Pokémon is no longer your opponent's Active Pokémon, this effect ends.)" to the end. Previously, the card had been interpreted as the effect lingering while on the Bench.