Win Condition:
The win condition of this deck is turn 7 Wrath of the Sea into animating Island Leviathan(s). This is possible through the Elementalist avatar providing the 8th water threshold. With a little chip damage early in the game, it can lead to an easy death's door and can ultimately finish off the opponent with Firebolts, Heat Ray, or Lightning bolt.
Sites:
When placing sites, you want to have a continuous body of water in your front sites. Doing this preps for Wrath of the Sea, allowing it to flood your whole side of the board and the front sites of your opponent to effectively wipe the board of all minions without submerge.
Floodplain helps this by turning your land sites into water sites, or expands your body of water into your opponent's sites. Floodplain also helps to fuel some combos that I will talk about later.
Island Leviathans go smack. They want to be in the front so they can attack the turn they animate.
Mirror Realm go smack.
Imperial Road wants to be held until the opponent has no sites in hand, so that the effect is one sided. Imperial Road can also act like a Tower and surprise the opponent with the sudden increase in mana.
Kingdom of Agartha protects from Earthquake and Bury. Also allows Diluvian Kraken to jump up from land sites which is the real reason its in this deck. Also does some fun stuff with Geistwood.
Geistwood is a great way to accrue extra value out of your Genesis minions. With floodplain you are able to flood it, put a Deep-sea Mermaid under it and it will die end of turn. Also you can do the opposite if you have Kingdom of Agartha active by burrowing a minion under Geistwood then flooding to kill the minion.
I believe that the rest of the sites are pretty self explanatory, but if someone would like me to go into them please leave a comment.
Auras:
Atlantean Fate is a great removal spell, but can also work as site hate to turn off the opponents threshold or key site abilities.
Artifacts:
Pnakotic Manuscript and Sunken Treasure Draw cards. Also Pnakotic Manuscript is another way to trigger Geistwood.
Spear of Destiny is there as a removal spell that can be used multiple times given the correct circumstances.
Minions:
Since there is a good number of different minions in the deck im going to cover them in groups.
Since the deck wants to make it to turn seven, it needs to play defensive until it can turn the corner. Wills-o'-the-Wisp and Tufted Turtles both can survive multiple attacks and usually require a removal spell before the opponent is able to progress. Tufted Turtles can also hold the Manuscript and draw each turn in the control match-up. Giant Shark also slows down the game when it hits the board and requires an answer if the opponent wants to make progress.
The card draw minions are Deep-sea Mermaids, Land Surveyor and Scavenging Fiend. Scavenging Fiend usually will bring back a sunken treasure, but could being back another artifact that was destroyed.
Tide Naiads are effectively a walking floodplain, but are also a spirit for Ghost Ship to being back. Anui Undine is currently in the list because of this reason. It is typically going to be smaller because this deck is not a mono water deck, but can death's door an opponent in combination with the Great Old One.
The remaining minions are the threats of the deck and how you kill the opponent if you don't see any Island Leviathans.
Ghost Ships can bring back dead Spirits, including each other which can allow for a very sticky treat in the late game.
Pudge Butcher can end a game by itself, but in combination with a Giant Shark, it can sometimes 1 shot the opponent.
Diluvian Kraken is mainly in the deck because it makes me happy when played with Kingdom of Agartha.
Great Old One isn't really needed, but is fun and can provide the threshold to animate Leviathans if a lot of land sites are clumped in the Atlas.
Lastly, Captain Baldassare has more than earned his spot in the deck. It's a card that can win the game by himself by giving you three extra cards a turn while also sometimes depriving the opponent of key cards.
Magic:
Common Sense is a tutor to help find Drown if a minion needs to be removed, but is typically used to find a Turtle to stall out the game or to find a finisher in Fire Bolts, Heat Ray or Lightning Bolt.
Plague of Frogs is probably the best stall card in the deck, and can draw 7 cards if used with the Manuscript.
Wrath of the Sea is probably the best card in the deck because it both clears the board and allows you to animate the Leviathans.
Revision History:
First Round of edits are to lower the curve of the deck, add more draw (testing Buried Treasure) and adding consistency to the Atlas with Crossroads.
Made the Common Sense Package a little bigger.
Considering Pnakotic Manuscript + Plague of Frogs instead of Buried Treasures.
Captain Baldassare was added for value, but I can see him being cut for a larger threat.
Edits:
-2 Mix Aqua
-2 Land Surveyor
-3 Anui Undine
-2 Atlas Wanderer
-2 Ghost Ship
-1 Maelstrom
-1 Undertow
+3 Buried Treasure
+4 Muck Lampreys
+1 Captain Baldassare
+1 Common Sense
+1 Firebolts
+1 Earthquake
+2 Crossroads
Second round of edits revert back to some old cards and add some new ones. Buried Treasure didn't perform as well as I hoped. It was awkward when I randomly had all water sites in my opener. Though Earthquake is a good card, it is not as good being used as a 5 mana reposition tool. I might try to slot in a blink or 2 to get a more efficient movement tool. Testing Queen of the Realm for draw power, as well as Manuscript Frogs.
Edits:
-3 Buried Treasure
-4 Muck Lampreys
-1 Earthquake
+2 Anui Undine
+2 Ghost Ship
+1 Plague of Frogs
+1 Pnakotic Manuscript
+1 Queen of the Realm
+1 Great Old One
Third round of edits I am removing some Scavenging Fiends so there are less dead cards sitting in hand. Can't remember the 3rd card taken out for this edit. Adding Tufted Turtles to help against Agro match-up. Also they work pretty well with Pnakotic Manuscript.
Edits:
-2 Scavenging Fiend
-1 Unknown (Lord of Unland?)
+3 Tufted Turtles
Fourth round of edits remove an Anui Undine since it isn't as large as it could be in this deck because of the 9 land Sites. I never drew Queen of the Realm, but I consistently have more cards in hand then my opponents so it wouldn't have been good in most games anyway, so it is being removed. The last removed card is a Pudge Butcher. Though Pudge is consistently a good card I want to test some other things.
The inclusions are Heat Ray, Wills-o'-the-Wisp and Spear of Destiny. Heat Ray as another good finisher spell, it might just fully replace fire bolts, but so far I have liked having both. Wills-o'-the-Wisp is another anti agro card that can typically survive for multiple blocks. Lastly, I just want to try Spear of Destiny to have a little more hard removal, as well as give my Frogs something else to do when they're just sitting there in the control match-up.
Edits:
-1 Anui Undine
-1 Pudge Butcher
-1 Queen of the Realm
+1 Heat Ray
+1 Spear of Destiny
+1 Wills-o'-the-Wisp
Fifth round of edits lower the curve a little adding another wisp for stalling and putting back in pudge as a more reliable threat. Blink might need to come back out for some more removal.
Edits:
-1 Anui Undine
-1 Spear of Destiny
-1 Firebolts
+1 Blink
+1 Pudge Butcher
+1 Wills-o'-the-Wisp