Haunter

Poké-BodyHidden Poison

If Haunter is your Active Pokémon and is damaged by an opponent's attack (even if Haunter is Knocked Out), the Attacking Pokémon is now Poisoned.

Choose 1 of your opponent's Pokémon. This attack does 20 damage to that Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)