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 this creature or enchanted creature deals combat damage to a player, draw a card.
Enchanted creature gets +3/+3.

Sapphire Medallion

Blue spells you cast cost {1} less to cast.

Benthic Behemoth

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

Kraken of the Straits

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

Scourge of Fleets

When this creature enters, 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.

Phantasmal Terrain

Enchant land
As this Aura enters, choose a basic land type.
Enchanted land is the chosen type.

Quicksilver Fountain

At the beginning of each player's upkeep, that player puts a flood counter on target non-Island land they control of their choice. That land is an Island for as long as it has a flood counter on it.
At the beginning of each end step, if all lands on the battlefield are Islands, remove all flood counters from them.

Guard Gomazoa

Defender, flying
Prevent all combat damage that would be dealt to this creature.

Dismiss

Reef Worm

When this creature dies, create a 3/3 blue Fish creature token with "When this token dies, create a 6/6 blue Whale creature token with 'When this token dies, create a 9/9 blue Kraken creature token.'"

Commander's Sphere

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

Dissipate

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

Deep-Sea Kraken

This creature can't be blocked.
Suspend 9—{2}{U} (Rather than cast this card from your hand, you may pay {2}{U} and exile it with nine time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost. It has haste.)
Whenever an opponent casts a spell, if this card is suspended, remove a time counter from it.

Displacement Wave

Return all nonland permanents with mana value X or less to their owners' hands.

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 this creature becomes monstrous, tap up to four target creatures. Those creatures don't untap during their controllers' untap steps for as long as you control this creature.

Beacon of Tomorrows

Target player takes an extra turn after this one. Shuffle Beacon of Tomorrows into its owner's library.

Infinite Reflection

Enchant creature
When this Aura enters attached to a creature, each other nontoken creature you control becomes a copy of that creature.
Nontoken creatures you control enter as a copy of enchanted creature.

Sealock Monster

This creature 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 this creature becomes monstrous, target land becomes an Island in addition to its other types.

Dreamstone Hedron

{T}: Add {C}{C}{C}.
{3}, {T}, Sacrifice this artifact: Draw three cards.

Aethersquall Ancient

Flying
At the beginning of your upkeep, you get {E}{E}{E} (three energy counters).
Pay eight {E}: Return all other creatures to their owners' hands. Activate only as a sorcery.

Colossal Whale

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever this creature attacks, you may exile target creature defending player controls until this creature leaves the battlefield. (That creature returns under its owner's control.)

Sky Diamond

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

Domineering Will

Target player gains control of up to three target nonattacking creatures until end of turn. Untap those creatures. They block this turn if able.

Unstable Obelisk

{T}: Add {C}.
{7}, {T}, Sacrifice this artifact: Destroy target permanent.

Streambed Aquitects

{T}: Target Merfolk creature gets +1/+1 and gains islandwalk until end of turn. (It can't be blocked as long as defending player controls an Island.)
{T}: Target land becomes an Island until end of turn.

Kefnet's Monument

Blue creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, target creature an opponent controls doesn't untap during its controller's next untap step.

Staff of the Mind Magus

Whenever you cast a blue spell or an Island you control enters, you gain 1 life.

Brine Elemental

Morph {5}{U}{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, each opponent skips their next untap step.

Fog Bank

Defender (This creature can't attack.)
Flying
Prevent all combat damage that would be dealt to and dealt by this creature.

Thran Dynamo

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.

Well of Ideas

When this enchantment enters, draw two cards.
At the beginning of each other player's draw step, that player draws an additional card.
At the beginning of your draw step, draw two additional cards.

Call to the Kindred

Enchant creature
At the beginning of your upkeep, you may look at the top five cards of your library. If you do, you may put a creature card that shares a creature type with enchanted creature from among them onto the battlefield, then you put the rest of those cards on the bottom of your library in any order.

Wonder

Flying
As long as this card is in your graveyard and you control an Island, creatures you control have flying.

Stormsurge Kraken

Hexproof
Lieutenant — As long as you control your commander, this creature gets +2/+2 and has "Whenever this creature becomes blocked, you may draw two cards."

Kraken Hatchling

Sleep

Tap all creatures target player controls. Those creatures don't untap during that player's next untap step.

Stormtide Leviathan

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
All lands are Islands in addition to their other types.
Creatures without flying or islandwalk can't attack.

Kederekt Leviathan

When this creature enters, return all other nonland permanents to their owners' hands.
Unearth {6}{U} ({6}{U}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Denizen of the Deep

When this creature enters, return each other creature you control to its owner's hand.

Island

Tideshaper Mystic

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

Gomazoa

Defender, flying
{T}: Put this creature and each creature it's blocking on top of their owners' libraries, then those players shuffle.

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.)

Sol Ring

Reef Shaman

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

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.

Fleet Swallower

Whenever this creature attacks, target player mills half their library, rounded up.

Inkwell Leviathan

Trample
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Shroud (This creature can't be the target of spells or abilities.)

Ur-Golem's Eye

Lorthos, the Tidemaker

Whenever Lorthos attacks, you may pay {8}. If you do, tap up to eight target permanents. Those permanents don't untap during their controllers' next untap steps.

Wall of Frost

Defender
Whenever this creature blocks a creature, that creature doesn't untap during its controller's next untap step.

Trench Gorger

Trample
When this creature enters, you may search your library for any number of land cards, exile them, then shuffle. If you do, this creature has base power and base toughness each equal to the number of cards exiled this way.

Breaching Leviathan

When this creature enters, if you cast it from your hand, tap all nonblue creatures. Those creatures don't untap during their controllers' next untap steps.

Cyclonic Rift

Return target nonland permanent you don't control to its owner's hand.
Overload {6}{U} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Slinn Voda, the Rising Deep

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
When Slinn Voda enters, if it was kicked, return all creatures to their owners' hands except for Merfolk, Krakens, Leviathans, Octopuses, and Serpents.

Tidal Warrior

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

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Karn's Temporal Sundering

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Target player takes an extra turn after this one. Return up to one target nonland permanent to its owner's hand. Exile Karn's Temporal Sundering.

Mistcaller

Sacrifice this creature: Until end of turn, if a nontoken creature would enter and it wasn't cast, exile it instead.

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.

Sand Squid

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

Tempt with Reflections

Tempting offer — Choose target creature you control. Create a token that's a copy of that creature. Each opponent may create a token that's a copy of that creature. For each opponent who does, create a token that's a copy of that 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}.