Sea's Claim

Enchant land (Target a land as you cast this. This card enters attached to that land.)
Enchanted land is an Island.

Star Compass

This artifact enters tapped.
{T}: Add one mana of any color that a basic land you control could produce.

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}.

Floodgate

Defender
When this creature has flying, sacrifice it.
When this creature leaves the battlefield, it deals damage to each nonblue creature without flying equal to half the number of Islands you control, rounded down.

Benthic Behemoth

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

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.

Distorting Wake

Return X target nonland permanents to their owners' hands.

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.

Sea Serpent

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

Deep-Sea Serpent

This creature can't attack unless defending player controls an Island.

Chambered Nautilus

Whenever this creature becomes blocked, you may draw a card.

Braingeyser

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.

Foil

You may discard an Island card and another card rather than pay this spell's mana cost.
Counter target spell.

Reef Shaman

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

Fact or Fiction

Reveal the top five cards of your library. An opponent separates those cards into two piles. Put one pile into your hand and the other into your graveyard.

Slipstream Eel

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

Killer Whale

{U}: This creature gains flying until end of turn.

Tidal Warrior

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

Lingering Mirage

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

Island

Segovian Leviathan

Ice Floe

You may choose not to untap this land during your untap step.
{T}: Tap target creature without flying that's attacking you. It doesn't untap during its controller's untap step for as long as this land remains tapped.

King Crab

{1}{U}, {T}: Put target green creature on top of its owner's library.

Sky Diamond

This artifact enters tapped.
{T}: Add {U}.

Horseshoe Crab

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}.

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.

Giant Crab

{U}: This creature gains shroud until end of turn. (It can't be the target of spells or abilities.)

Annex

Enchant land (Target a land as you cast this. This card enters attached to that land.)
You control enchanted land.

Sea Scryer

Great Whale

When this creature enters, untap up to seven lands.

Svyelunite Temple

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

Control Magic

Enchant creature
You control enchanted creature.

Island Fish Jasconius

This creature doesn't untap during your untap step.
At the beginning of your upkeep, you may pay {U}{U}{U}. If you do, untap this creature.
This creature can't attack unless defending player controls an Island.
When you control no Islands, sacrifice this creature.

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}.

Narwhal

Dandân

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.

Rushing River

Kicker—Sacrifice a land. (You may sacrifice a land in addition to any other costs as you cast this spell.)
Return target nonland permanent to its owner's hand. If this spell was kicked, return another target nonland permanent to its owner's hand.

Wash Out

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

Counterspell

Manta Ray

This creature can't attack unless defending player controls an Island.
This creature can't be blocked except by blue creatures.
When you control no Islands, sacrifice this creature.

Seafloor Debris

This land enters tapped.
{T}: Add {U}.
{T}, Sacrifice this land: Add one mana of any color.

Sand Squid

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
You may choose not to untap Sand Squid during your untap step.
{T}: Tap target creature. That creature doesn't untap during its controller's untap step for as long as Sand Squid remains tapped.

Seasinger

When you control no Islands, sacrifice this creature.
You may choose not to untap this creature during your untap step.
{T}: Gain control of target creature whose controller controls an Island for as long as you control this creature and this creature remains tapped.

Coral Eel

Remote Isle

This land enters tapped.
{T}: Add {U}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Thing from the Deep

Whenever this creature attacks, sacrifice it unless you sacrifice an Island.

Lonely Sandbar

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

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.

Giant Octopus

Aboshan, Cephalid Emperor

Tap an untapped Octopus you control: Tap target permanent.
{U}{U}{U}: Tap all creatures without flying.

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.

Coastal Piracy

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

Gush

You may return two Islands you control to their owner's hand rather than pay this spell's mana cost.
Draw two cards.

Sol Ring

Man-o'-War

When this creature enters, return target creature to its owner's hand.

Horned Turtle

Equilibrium

Whenever you cast a creature spell, you may pay {1}. If you do, return target creature to its owner's hand.

Hammerhead Shark

High Tide

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

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.

Conch Horn

{1}, {T}, Sacrifice this artifact: Draw two cards, then put a card from your hand on top of your library.

Sea Snidd

Sunken City

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

Empress Galina

{U}{U}, {T}: Gain control of target legendary permanent. (This effect lasts indefinitely.)

Capsize

Buyback {3} (You may pay an additional {3} as you cast this spell. If you do, put this card into your hand as it resolves.)
Return target permanent to its owner's hand.

Sea Monster

Tolaria

{T}: Add {U}.
{T}: Target creature loses banding and all "bands with other" abilities until end of turn. Activate only during any upkeep step.

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.

Evacuation

Return all creatures to their owners' hands.

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.