As long as this Pokémon is in the Active Spot, your opponent can't have more than 3 Benched Pokémon. If they have 4 or more Benched Pokémon, they discard Benched Pokemon until they have 3 Pokemon on the Bench. If more than one effect changes the number of Benched Pokémon allowed, use the smaller number:

• Poisonous Gem

  140

  Your opponent's Active Pokémon is now Poisoned.