Blue Mana Battery

{2}, {T}: Put a charge counter on this artifact.
{T}, Remove any number of charge counters from this artifact: Add {U}, then add an additional {U} for each charge counter removed this way.

Homarid

This creature enters with a tide counter on it.
At the beginning of your upkeep, put a tide counter on this creature.
As long as there is exactly one tide counter on this creature, it gets -1/-1.
As long as there are exactly three tide counters on this creature, it gets +1/+1.
Whenever there are four or more tide counters on this creature, remove all tide counters from it.

Merfolk Looter

Sea Scryer

Walking Sponge

{T}: Target creature loses your choice of flying, first strike, or trample until end of turn.

Taniwha

Trample
Phasing (This phases in or out before you untap during each of your untap steps. While it's phased out, it's treated as though it doesn't exist.)
At the beginning of your upkeep, all lands you control phase out. (They phase in before you untap during your next untap step.)

Vodalian Mage

{U}, {T}: Counter target spell unless its controller pays {1}.

Tidal Warrior

{T}: Target land becomes an Island until end of turn.

Water Wurm

This creature gets +0/+1 as long as an opponent controls an Island.

Reef Shaman

{T}: Target land becomes the basic land type of your choice until end of turn.

Reveka, Wizard Savant

{T}: Reveka deals 2 damage to any target and doesn't untap during your next untap step.

Fishliver Oil

Enchant creature (Target a creature as you cast this. This card enters attached to that creature.)
Enchanted creature has islandwalk. (It can't be blocked as long as defending player controls an Island.)

Sea Serpent

This creature can't attack unless defending player controls an Island.
When you control no Islands, sacrifice this creature.

Devouring Deep

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Traveler's Cloak

Enchant creature
As this Aura enters, choose a land type.
When this Aura enters, draw a card.
Enchanted creature has landwalk of the chosen type. (It can't be blocked as long as defending player controls a land of that type.)

Dandân

Tidal Flats

{U}{U}: For each attacking creature without flying, its controller may pay {1}. If that player doesn't, creatures you control blocking that creature gain first strike until end of turn.

Part Water

X target creatures gain islandwalk until end of turn. (They can't be blocked as long as defending player controls an Island.)

Arcane Denial

Counter target spell. Its controller may draw up to two cards at the beginning of the next turn's upkeep.
You draw a card at the beginning of the next turn's upkeep.

Svyelunite Temple

This land enters tapped.
{T}: Add {U}.
{T}, Sacrifice this land: Add {U}{U}.

Land Equilibrium

If an opponent who controls at least as many lands as you do would put a land onto the battlefield, that player instead puts that land onto the battlefield then sacrifices a land of their choice.

Tidal Influence

Cast this spell only if no permanents named Tidal Influence are on the battlefield.
This enchantment enters with a tide counter on it.
At the beginning of your upkeep, put a tide counter on this enchantment.
As long as there is exactly one tide counter on this enchantment, all blue creatures get -2/-0.
As long as there are exactly three tide counters on this enchantment, all blue creatures get +2/+0.
Whenever there are four or more tide counters on this enchantment, remove all tide counters from it.

Theft of Dreams

Draw a card for each tapped creature target opponent controls.

Deep Spawn

Trample
At the beginning of your upkeep, sacrifice this creature unless you mill two cards.
{U}: This creature gains shroud until end of turn and doesn't untap during your next untap step. Tap this creature. (A creature with shroud can't be the target of spells or abilities.)

Polar Kraken

Trample
This creature enters tapped.
Cumulative upkeep—Sacrifice a land. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)

Well of Knowledge

{2}: Draw a card. Any player may activate this ability but only during their draw step.

Pirate Ship

This creature can't attack unless defending player controls an Island.
{T}: This creature deals 1 damage to any target.
When you control no Islands, sacrifice this creature.

Coral Atoll

This land enters tapped.
When this land enters, sacrifice it unless you return an untapped Island you control to its owner's hand.
{T}: Add {C}{U}.

Rush of Knowledge

Draw cards equal to the greatest mana value among permanents you control.

Narwhal

Sandals of Abdallah

{2}, {T}: Target creature gains islandwalk until end of turn. When that creature dies this turn, destroy this artifact. (A creature with islandwalk can't be blocked as long as defending player controls an Island.)

Submerge

If an opponent controls a Forest and you control an Island, you may cast this spell without paying its mana cost.
Put target creature on top of its owner's library.

Magical Hack

Change the text of target spell or permanent by replacing all instances of one basic land type with another. (For example, you may change "swampwalk" to "plainswalk." This effect lasts indefinitely.)

Sand Silos

This land enters tapped.
You may choose not to untap this land during your untap step.
At the beginning of your upkeep, if this land is tapped, put a storage counter on it.
{T}, Remove any number of storage counters from this land: Add {U} for each storage counter removed this way.

Slipstream Eel

This creature can't attack unless defending player controls an Island.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)

Saprazzan Skerry

This land enters tapped with two depletion counters on it.
{T}, Remove a depletion counter from this land: Add {U}{U}. If there are no depletion counters on this land, sacrifice it.

Wash Out

Return all permanents of the color of your choice to their owners' hands.

Snap

Return target creature to its owner's hand. Untap up to two lands.

Mana Vortex

When you cast this spell, counter it unless you sacrifice a land.
At the beginning of each player's upkeep, that player sacrifices a land of their choice.
When there are no lands on the battlefield, sacrifice this enchantment.

Saprazzan Heir

Whenever this creature becomes blocked, you may draw three cards.

Keep Watch

Energy Tap

Tap target untapped creature you control. If you do, add an amount of {C} equal to that creature's mana value.

Kukemssa Serpent

This creature can't attack unless defending player controls an Island.
{U}, Sacrifice an Island: Target land an opponent controls becomes an Island until end of turn.
When you control no Islands, sacrifice this creature.

Giant Shark

This creature can't attack unless defending player controls an Island.
Whenever this creature blocks or becomes blocked by a creature that has been dealt damage this turn, this creature gets +2/+0 and gains trample until end of turn.
When you control no Islands, sacrifice this creature.

Whirlpool Rider

When this creature enters, shuffle the cards from your hand into your library, then draw that many cards.

Mystic Remora

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Teferi's Isle

Phasing (This phases in or out before you untap during each of your untap steps. While it's phased out, it's treated as though it doesn't exist.)
Teferi's Isle enters tapped.
{T}: Add {U}{U}.

Marjhan

This creature doesn't untap during your untap step.
{U}{U}, Sacrifice a creature: Untap this creature. Activate only during your upkeep.
This creature can't attack unless defending player controls an Island.
{U}{U}: This creature gets -1/-0 until end of turn and deals 1 damage to target attacking creature without flying.
When you control no Islands, sacrifice this creature.

War Barge

{3}: Target creature gains islandwalk until end of turn. When this artifact leaves the battlefield this turn, destroy that creature. A creature destroyed this way can't be regenerated. (A creature with islandwalk can't be blocked as long as defending player controls an Island.)

Spiny Starfish

{U}: Regenerate this creature.
At the beginning of each end step, if this creature regenerated this turn, create a 0/1 blue Starfish creature token for each time it regenerated this turn.

Iceberg

This enchantment enters with X ice counters on it.
{3}: Put an ice counter on this enchantment.
Remove an ice counter from this enchantment: Add {C}.

Power Sink

Counter target spell unless its controller pays {X}. If that player doesn't, they tap all lands with mana abilities they control and lose all unspent mana.

Sol Ring

Lingering Mirage

Enchant land
Enchanted land is an Island.
Cycling {2} ({2}, Discard this card: Draw a card.)

Giant Octopus

High Tide

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.

Coral Reef

This enchantment enters with four polyp counters on it.
Sacrifice an Island: Put two polyp counters on this enchantment.
{U}, Tap an untapped blue creature you control, Remove a polyp counter from this enchantment: Put a +0/+1 counter on target creature.

Benthic Behemoth

Merseine

Enchant creature
This Aura enters with three net counters on it.
Enchanted creature doesn't untap during its controller's untap step if this Aura has a net counter on it.
Pay enchanted creature's mana cost: Remove a net counter from this Aura. Only the controller of the enchanted creature may activate this ability.

Island

Tangle Kelp

Enchant creature
When this Aura enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step if it attacked during its controller's last turn.

Vodalian Soldiers

Chromeshell Crab

Morph {4}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When this creature is turned face up, you may exchange control of target creature you control and target creature an opponent controls.

Siren's Call

Cast this spell only during an opponent's turn, before attackers are declared.
Creatures the active player controls attack this turn if able.
At the beginning of the next end step, destroy all non-Wall creatures that player controls that didn't attack this turn. Ignore this effect for each creature the player didn't control continuously since the beginning of the turn.

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Wall of Kelp

Defender (This creature can't attack.)
{U}{U}, {T}: Create a 0/1 blue Plant Wall creature token with defender named Kelp.

Flux

Each player discards any number of cards, then draws that many cards.
Draw a card.

Eye of Ramos

{T}: Add {U}.
Sacrifice this artifact: Add {U}.

Sunken City

At the beginning of your upkeep, sacrifice this enchantment unless you pay {U}{U}.
Blue creatures get +1/+1.

Lord of Atlantis

Other Merfolk get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Veiled Serpent

When an opponent casts a spell, if this permanent is an enchantment, it becomes a 4/4 Serpent creature with "This creature can't attack unless defending player controls an Island."
Cycling {2} ({2}, Discard this card: Draw a card.)

Helm of Awakening

Howling Mine

At the beginning of each player's draw step, if this artifact is untapped, that player draws an additional card.

Lonely Sandbar

This land enters tapped.
{T}: Add {U}.
Cycling {U} ({U}, Discard this card: Draw a card.)

Mystic Veil

You may cast this spell as though it had flash. If you cast it any time a sorcery couldn't have been cast, the controller of the permanent it becomes sacrifices it at the beginning of the next cleanup step.
Enchant creature
Enchanted creature has shroud. (It can't be the target of spells or abilities.)

Coastal Piracy

Whenever a creature you control deals combat damage to an opponent, you may draw a card.

Chain Stasis

You may tap or untap target creature. Then that creature's controller may pay {2}{U}. If the player does, they may copy this spell and may choose a new target for that copy.

Giant Oyster

You may choose not to untap this creature during your untap step.
{T}: For as long as this creature remains tapped, target tapped creature doesn't untap during its controller's untap step, and at the beginning of each of your draw steps, put a -1/-1 counter on that creature. When this creature leaves the battlefield or becomes untapped, remove all -1/-1 counters from the creature.

Thawing Glaciers

This land enters tapped.
{1}, {T}: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle. Return this land to its owner's hand at the beginning of the next cleanup step.

Thalakos Mistfolk

Shadow (This creature can block or be blocked by only creatures with shadow.)
{U}: Put this creature on top of its owner's library.

Lilting Refrain

At the beginning of your upkeep, you may put a verse counter on this enchantment.
Sacrifice this enchantment: Counter target spell unless its controller pays {X}, where X is the number of verse counters on this enchantment.

Scent of Brine

Reveal any number of blue cards in your hand. Counter target spell unless its controller pays {1} for each card revealed this way.