Or, you can Normal Summon "Deep Sea Diva" to Special Summon "Spined Gillman while this card is already face-up, increasing its ATK by another 400 points.
Normal Summon "Hammer Shark" and use its effect to Summon out this Card. Both are now Level 3 and ready for an Xyz Summon, or, attack with a 1700 ATK "Hammerhead" and 2200 ATK beater.
Normal Summon "Atlantean Marksman" and inflict damage with it. Then, Special Summon this card from the deck with his effect. Since "Marksman" is already face-up, "Atlantean Attack Squad" will be at 2200 ATK already, after which you may overlay into "Number 17: Leviathan Dragon", destroying an opponent's face-down card with "Marksman's" effect that triggers when detached. If you have Normal Summoned "Deep Sea Diva" that turn, you can also Synchro Summon a level 8 monster such as "Scrap Dragon" or "Stardust Dragon".