If I use Bruxish's "Synchronoise" attack against my opponent's dual type Pokemon like Volcanion EX, and there are other Volcanion EX on the Bench, do they take 40 damage or 20?
They take 20 damage.
Synchronoise



x2
Gnash TeethYour opponent's Active Pokémon is now Confused.


SynchronoiseThis attack does 20 damage to each of your opponent's Benched Pokémon that shares a type with your opponent's Active Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)
If I use Bruxish's "Synchronoise" attack against my opponent's dual type Pokemon like Volcanion EX, and there are other Volcanion EX on the Bench, do they take 40 damage or 20?
They take 20 damage.