Tidal Wave

Create a 5/5 blue Wall creature token with defender. Sacrifice it at the beginning of the next end step.

Thassa's Emissary

Bestow {5}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Whenever Thassa's Emissary or enchanted creature deals combat damage to a player, draw a card.
Enchanted creature gets +3/+3.

Chariot of Victory

Equipped creature has first strike, trample, and haste.
Equip {1}

Sea God's Scorn

Return up to three target creatures and/or enchantments to their owners' hands.

Ordeal of Thassa

Enchant creature
Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice Ordeal of Thassa.
When you sacrifice Ordeal of Thassa, draw two cards.

Nimbus Naiad

Bestow {4}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Flying
Enchanted creature gets +2/+2 and has flying.

Memory Drain

Siren of the Fanged Coast

Flying
Tribute 3 (As this creature enters the battlefield, an opponent of your choice may put three +1/+1 counters on it.)
When Siren of the Fanged Coast enters the battlefield, if tribute wasn't paid, gain control of target creature.

Sol Ring

Shoal Kraken

Constellation — Whenever an enchantment enters the battlefield under your control, you may draw a card. If you do, discard a card.

Tromokratis

Tromokratis has hexproof unless it's attacking or blocking.
Tromokratis can't be blocked unless all creatures defending player controls block it. (If any creature that player controls doesn't block this creature, it can't be blocked.)

Aerie Worshippers

Inspired — Whenever Aerie Worshippers becomes untapped, you may pay {2}{U}. If you do, create a 2/2 blue Bird enchantment creature token with flying.

Altar of the Pantheon

Your devotion to each color and each combination of colors is increased by one.
{T}: Add one mana of any color. If you control a God, a Demigod, or a legendary enchantment, you gain 1 life.

Sea God's Revenge

Return up to three target creatures your opponents control to their owners' hands. Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Thassa's Rebuff

Counter target spell unless its controller pays {X}, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Whelming Wave

Return all creatures to their owners' hands except for Krakens, Leviathans, Octopuses, and Serpents.

Cloaked Siren

Flash (You may cast this spell any time you could cast an instant.)
Flying

Triton Fortune Hunter

Heroic — Whenever you cast a spell that targets Triton Fortune Hunter, draw a card.

Pull from the Deep

Return up to one target instant card and up to one target sorcery card from your graveyard to your hand. Exile Pull from the Deep.

Island

Pin to the Earth

Enchant creature
Enchanted creature gets -6/-0.

Scourge of Fleets

When Scourge of Fleets enters the battlefield, return each creature your opponents control with toughness X or less to its owner's hand, where X is the number of Islands you control.

Sudden Storm

Tap up to two target creatures. Those creatures don't untap during their controllers' next untap steps. Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Triton Tactics

Up to two target creatures each get +0/+3 until end of turn. Untap those creatures. At this turn's next end of combat, tap each creature that was blocked by one of those creatures this turn and it doesn't untap during its controller's next untap step.

Thassa, Deep-Dwelling

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature.
At the beginning of your end step, exile up to one other target creature you control, then return that card to the battlefield under your control.
{3}{U}: Tap another target creature.

Opaline Unicorn

Nadir Kraken

Whenever you draw a card, you may pay {1}. If you do, put a +1/+1 counter on Nadir Kraken and create a 1/1 blue Tentacle creature token.

Archetype of Imagination

Creatures you control have flying.
Creatures your opponents control lose flying and can't have or gain flying.

Fated Infatuation

Create a token that's a copy of target creature you control. If it's your turn, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Thassa's Bounty

Draw three cards. Target player mills three cards.

Divination

Swan Song

Counter target enchantment, instant, or sorcery spell. Its controller creates a 2/2 blue Bird creature token with flying.

One with the Stars

Enchant creature or enchantment
Enchanted permanent is an enchantment and loses all other card types. (It still has its abilities, but it's no longer a creature.)

Thassa's Ire

{3}{U}: You may tap or untap target creature.

Countermand

Counter target spell. Its controller mills four cards.

Callaphe, Beloved of the Sea

Callaphe's power is equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
Creatures and enchantments you control have "Spells your opponents cast that target this permanent cost {1} more to cast."

Hall of Triumph

As Hall of Triumph enters the battlefield, choose a color.
Creatures you control of the chosen color get +1/+1.

Shipbreaker Kraken

{6}{U}{U}: Monstrosity 4. (If this creature isn't monstrous, put four +1/+1 counters on it and it becomes monstrous.)
When Shipbreaker Kraken becomes monstrous, tap up to four target creatures. Those creatures don't untap during their controllers' untap steps for as long as you control Shipbreaker Kraken.

Font of Fortunes

{1}{U}, Sacrifice Font of Fortunes: Draw two cards.

Sleep of the Dead

Tap target creature. It doesn't untap during its controller's next untap step.
Escape—{2}{U}, Exile three other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Nyxborn Triton

Bestow {4}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Enchanted creature gets +2/+3.

Nyxborn Seaguard

Naiad of Hidden Coves

As long as it's not your turn, spells you cast cost {1} less to cast.

Thryx, the Sudden Storm

Flash
Flying
Spells you cast with mana value 5 or greater cost {1} less to cast and can't be countered.

Kraken of the Straits

Creatures with power less than the number of Islands you control can't block Kraken of the Straits.

Evanescent Intellect

Enchant creature
Enchanted creature has "{1}{U}, {T}: Target player mills three cards."

Griptide

Put target creature on top of its owner's library.

Fate Foretold

Enchant creature
When Fate Foretold enters the battlefield, draw a card.
When enchanted creature dies, its controller draws a card.

Annul

Counter target artifact or enchantment spell.

Siren Song Lyre

Equipped creature has "{2}, {T}: Tap target creature."
Equip {2}

Omen of the Sea

Flash
When Omen of the Sea enters the battlefield, scry 2, then draw a card.
{2}{U}, Sacrifice Omen of the Sea: Scry 2.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Sealock Monster

Sealock Monster can't attack unless defending player controls an Island.
{5}{U}{U}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
When Sealock Monster becomes monstrous, target land becomes an Island in addition to its other types.

Nullify

War-Wing Siren

Flying
Heroic — Whenever you cast a spell that targets War-Wing Siren, put a +1/+1 counter on War-Wing Siren.

Aerial Formation

Strive — This spell costs {2}{U} more to cast for each target beyond the first.
Any number of target creatures each get +1/+1 and gain flying until end of turn.

Deny the Divine

Counter target creature or enchantment spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Thassa's Oracle

When Thassa's Oracle enters the battlefield, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Nykthos, Shrine to Nyx

{T}: Add {C}.
{2}, {T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)

Nyx Lotus

Nyx Lotus enters the battlefield tapped.
{T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)

Unknown Shores

{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Towering-Wave Mystic

Whenever Towering-Wave Mystic deals damage, target player mills that many cards.

Thassa, God of the Sea

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
At the beginning of your upkeep, scry 1.
{1}{U}: Target creature you control can't be blocked this turn.

Thassa's Devourer

Constellation — Whenever Thassa's Devourer or another enchantment enters the battlefield under your control, target player mills two cards.

Thassa's Intervention

Choose one —
• Look at the top X cards of your library. Put up to two of them into your hand and the rest on the bottom of your library in a random order.
• Counter target spell unless its controller pays twice {X}.

Bident of Thassa

Whenever a creature you control deals combat damage to a player, you may draw a card.
{1}{U}, {T}: Creatures your opponents control attack this turn if able.

Benthic Giant

Hexproof (This creature can't be the target of spells or abilities your opponents control.)

Crystalline Nautilus

Bestow {3}{U}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
When Crystalline Nautilus becomes the target of a spell or ability, sacrifice it.
Enchanted creature gets +4/+4 and has "When this creature becomes the target of a spell or ability, sacrifice it."

Eidolon of Philosophy

{6}{U}, Sacrifice Eidolon of Philosophy: Draw three cards.

Dissolve

Counter target spell. Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Evolving Wilds

{T}, Sacrifice Evolving Wilds: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Floodtide Serpent

Floodtide Serpent can't attack unless you return an enchantment you control to its owner's hand. (This cost is paid as attackers are declared.)

Whitewater Naiads

Constellation — Whenever Whitewater Naiads or another enchantment enters the battlefield under your control, target creature can't be blocked this turn.

Sigiled Starfish

{T}: Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)