Turns out being able to wipe the board on Turn 2 with a single card is pretty good. Aside from the monster in your hand for Level Augmentation, all you need to Summon a Level 7 Synchro is Deep Sea Diva. That’s definitely a pretty big step up from Summoning Armades, Keeper of Boundaries using Junk Synchron. Keep in mind that you can only use your Skill once.
Use Abyss-sphere to Special Summon Mermail Abysslinde. If Abyss-sphere leaves the field, Abysslinde will be destroyed and it will allow you to Special Summon a “Mermail” monster from your Deck. Even if nothing happens to Abyss-sphere, during the next End Phase of your opponent’s turn after its activation, the Continuous Trap will destroy itself. Keep in mind that, if your opponent responds to the activation of Abyss-sphere by activating Cosmic Cyclone, banishing the Continuous Trap, you don’t get to Special Summon any monster.
You can use Mermail Abysslinde’s effect to Special Summon Mermail Abysspike and then use Abysspike’s effect to add a Level 3 WATER monster from your Deck to your hand.
If you activate Abysspike’s effect by discarding Atlantean Marksman, you will get to the target and destroy a face-up card your opponent controls.
Keep in mind that, if you target a face-up “Subterror” monster and your opponent response by activating Subterror Final Battle and changing that monster to face-down Defense Position, the monster will not be destroyed because it’s not a suitable target anymore.
Keep in mind that, if you target a face-down Spell/Trap Card and your opponent activates it in response, the card will not be destroyed because it’s not a suitable target anymore.
You can just Normal Summon Mermail Abysspike, discard Abyssgunde, Special Summon Mermail Abyssmegalo from your Graveyard and then utilize Abysspike to activate its effect. If you want the monster Special Summoned by Abyss-sphere to stay on the field, you can activate it during your opponent’s End Phase.
You could also use the Continuous Trap to Special Summon Mermail Abyssmegalo or Abyssteus, but you wouldn’t get much value out of them since even Dragon Spirit of White and Legendary Six Samurai - Shi En are able to get over them without Beatdown! or The Tie that Binds.
You can Special Summon Mermail Abyssmegalo from your hand by discarding two WATER monsters. By discarding Atlantean Marksman, Heavy Infantry or Mermail Abyssgunde, you can get back some value from the resources you’ve invested to Summon Abyssmegalo.
When it’s Special Summoned by its own effect, Mermail Abyssmegalo allows you to add an “Abyss-” Spell/Trap Card from your Deck to your hand. You can use Abyssmegalo’s effect to search Abyss-sphere, which I’ve already talked about.
Unlike Abyssmegalo, Abyssteus requires you to discard only one WATER monster in order to be Summoned and, to make it even more cost-efficient, it also allows you to add a Level 4 or lower “Mermail” monster from your Deck to your hand when it’s Summoned this way.
This Skill notably increases the value of Deep Sea Diva, turning it into pretty much any Synchro Monster in your Extra Deck.