Gyarados

This attack does 10 damage to each of your opponent's Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)

Does 20 damage times the number of damage counters on all of your Magikarp.

If the Defending Pokémon already has at least 2 damage counters on it, this attack does 50 damage plus 50 more damage.