Mermail Shadow Squad (Ultra Rare)

(This card is always treated as an Atlantean card.)
You can discard 1 card to the GY; the Levels of all WATER monsters you currently control become 7 until the end of this turn. If this card is sent to the GY to activate a WATER monster's effect: Special Summon 1 Level 4 or lower Atlantean or Mermail monster from your Deck, except Mermail Shadow Squad, also you cannot Special Summon from the Extra Deck for the rest of this turn, except WATER monsters. You can only use each effect of Mermail Shadow Squad once per turn.