Atlantean Heavy Infantry

While this card is face-up on the field, once per turn during your Main Phase, you can Normal Summon a Level 4 or lower Sea Serpent-Type monster in addition to your Normal Summon or Set. (You can only gain this effect once per turn.) When this card is sent to the Graveyard for the activation of a WATER monster's effect: Target 1 face-up card your opponent controls; destroy that target.