Trinity Merlantean May 2021

This is a mild reimagining of the Trinity Merlantean Deck featured in this video:  How to play Mermail【Trinity Yu-Gi-Oh!】 - YouTube
Many of the combos and tech featured in this video remain relevant.

3 cards released since this video introduce major new lines, Mermail Abyssalacia, Ravenous Crocodragon Archethys, and Adamancipator Risen - Dragite
These cards are all notable because they introduce solid first turn plays, Abyssalacia and Crocodragon can both discard Atlantean Heavy Infantry as the cost for a quick effect, giving an effective single or double pop respectively. Dragite is just a Spell Negate, which can be incredibly threatening against many decks.

Abyssalacia can be made with any 2 monsters in the Merlantean typings (Fish, Aqua, Sea Serpent), but is best setup by Deep Sea Diva summoning Neptabyss, whose effect gives you Atlanteans to discard for Abyssalacia's cost.

Crocodragon is more difficult to make, as a Level 9 Synchro, the only really consistent setup in the deck is having Mermail Abysspike discard Dragoons as cost, searching Lappis Dragon as well as a Level 3 WATER monster. This setup can also make Abyssalacia if needed, which is sometimes relevant for her float effect.

Finally, Dragite is made turn 1 off of Genex Undine. Once again you dump Dragoons to add Lappis Dragon, but having one less level you can make a Synchro 8. The deck is on no Rocks for the first effect, though you can still activate it if you want to get the top 5 cards to the bottom of your deck, for some reason? Once again, this setup can make Abyssalacia if needed.

A final thing of note is that much of this deck is "dumb" techs. The Gorz-likes have been mostly fine in my play, though running Ra and not just Guardian Slime is somewhat suspect. In all my play of this deck I have not resolves Cataclysmic Circumpolar Chillbania once, and am leaning to it being a bad card. Additionally, LANphorynchus is entirely unneeded in this build, it carried over from builds on more complex Undine combos that did need it, but I would not run it in hindsight.