Mermail Abyssbalaen

① You can discard 4 other "Mermail" monsters to the GY; Special Summon this card from your hand.
② If you do: Target cards your opponent controls, up to the number of "Mermail" monsters in your GY (if possible);
even if nothing was targeted, this card gains 500 ATK, and if it does, destroy those targets (if any).
③ You can Tribute 1 other face-up Attack Position "Mermail" monster; this turn, this card gains this effect.
● At the start of the Damage Step, if this card battles a Defense Position monster: Destroy that monster.