Leviathan

Trample
This creature enters tapped and doesn't untap during your untap step.
At the beginning of your upkeep, you may sacrifice two Islands. If you do, untap this creature.
This creature can't attack unless you sacrifice two Islands. (This cost is paid as attackers are declared.)

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.

Pearl Lake Ancient

Flash
This spell can't be countered.
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Return three lands you control to their owner's hand: Return this creature to its owner's hand.

Kiora, Behemoth Beckoner

Whenever a creature you control with power 4 or greater enters, draw a card.
−1: Untap target permanent.

Dispersal Shield

Counter target spell if its mana value is less than or equal to the highest mana value among permanents you control.

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.

Imoti, Celebrant of Bounty

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Spells you cast with mana value 6 or greater have cascade.

Sunken City

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

Nadir Kraken

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

Harbor Serpent

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
This creature can't attack unless there are five or more Islands on the battlefield.

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.)

Wormhole Serpent

{3}{U}: Target creature can't be blocked this turn.

Homarid Warrior

{U}: This creature gains shroud until end of turn and doesn't untap during your next untap step. Tap it. (A creature with shroud can't be the target of spells or abilities.)

Sea Serpent

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

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.)

Wash Away

Cleave {1}{U}{U} (You may cast this spell for its cleave cost. If you do, remove the words in square brackets.)
Counter target spell [that wasn't cast from its owner's hand].

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.

Junk Winder

Affinity for tokens (This spell costs {1} less to cast for each token you control.)
Whenever a token you control enters, tap target nonland permanent an opponent controls. It doesn't untap during its controller's next untap step.

Tolarian Terror

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)

Thirst for Discovery

Draw three cards. Then discard two cards unless you discard a basic land card.

Archetype of Imagination

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

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.

Homarid Spawning Bed

{1}{U}{U}, Sacrifice a blue creature: Create X 1/1 blue Camarid creature tokens, where X is the sacrificed creature's mana value.

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.

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.