Flip a coin. If heads, this attack does 10 damage plus 10 more damage; if tails, this attack does 10 damage.
If you have any Benched Pokémon, flip a coin. If tails, choose 1 of your Benched Pokémon. This attack does 20 damage to that Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)