Neo-Spacian Aqua Dolphin (POTD-EN003) [Power of the Duelist]

Once per turn, by discarding 1 card from your hand, look at your opponent's hand and select 1 Monster Card in it. If there is a monster on your side of the field with ATK greater than or equal to the ATK of the selected monster, destroy the selected Monster Card and inflict 500 damage to your opponent. If there is no monster on your side of the field with ATK greater than or equal to the ATK of the selected monster, take 500 damage.