If Cacnea has any Darkness Energy attached to it, this attack does 10 damage plus 10 more damage.
Flip 2 coins. For each heads, choose 1 of your opponent's Pokémon and this attack does 10 damage to that Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.) (You can choose the same Pokémon more than once, but you can't do more than 10 damage to that Pokémon in this way.)