Crystal Shark

If this card is in your hand or GY: You can target 1 WATER monster on the field; you cannot Special Summon monsters from the Extra Deck for the rest of this turn, except Xyz Monsters, also Special Summon this card (but banish it when it leaves the field), and if you do, the targeted monster's current ATK becomes halved. You can only use this effect of "Crystal Shark" once per turn. If this card is used for the Xyz Summon of a "Number" monster, it can be treated as a Level 3 or 4 monster.