You can use "Abyss-sphere" to Summon "Mermail Abysslinde" from your Deck during your opponent's turn, and when "Abysslinde" is sent to the Graveyard, you can use its effect to Special Summon this card.
By discarding "Mermail Abyssgunde" with this card's effect, you can revive another Level 7 "Meramail" monster in order to perform an Xyz Summon.
Discard "Neptabyss" and "Heavy Infantry"/"Marksman" to Special Summon this card; use the effect of "Marksman" or "Heavy Infantry" to destroy an opponent's card, and chain the effect "Neptabyss" to Special Summon (in Attack Position) the other discarded "Atlantean" monster. Tribute the monster Special Summoned by "Neptabyss" so that you can use its destruction effect once more while also allowing this card to attack twice.
By using the effect of "Number 47: Nightmare Shark" on this card, and then tributing it for this card's effect, this card can attack your opponent twice directly, possibly inflicting 4800 damage.