Fellwar Stone

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

Mulldrifter

Flying
When Mulldrifter enters the battlefield, draw two cards.
Evoke {2}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters the battlefield.)

Treasure Hunt

Reveal cards from the top of your library until you reveal a nonland card, then put all cards revealed this way into your hand.

Spiny Starfish

{U}: Regenerate Spiny Starfish.
At the beginning of each end step, if Spiny Starfish regenerated this turn, create a 0/1 blue Starfish creature token for each time it regenerated this 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 Chromeshell Crab is turned face up, you may exchange control of target creature you control and target creature an opponent controls.

Aboshan, Cephalid Emperor

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

Sea Gate Oracle

When Sea Gate Oracle enters the battlefield, look at the top two cards of your library. Put one of them into your hand and the other on the bottom of your library.

Iceberg Cancrix

Whenever another snow permanent enters the battlefield under your control, you may have target player mill two cards.

Ruin Crab

Landfall — Whenever a land enters the battlefield under your control, each opponent mills three cards. (To mill a card, a player puts the top card of their library into their graveyard.)

Aegis Turtle

Giant Octopus

High Tide

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

Horned Turtle

Sky Diamond

Sky Diamond enters the battlefield tapped.
{T}: Add {U}.

Countervailing Winds

Counter target spell unless its controller pays {1} for each card in your graveyard.
Cycling {2} ({2}, Discard this card: Draw a card.)

Ancient Crab

Thought Sponge

Flash
Thought Sponge enters the battlefield with a number of +1/+1 counters on it equal to the greatest number of cards an opponent has drawn this turn.
When Thought Sponge dies, draw cards equal to its power.

Devastation Tide

Return all nonland permanents to their owners' hands.
Miracle {1}{U} (You may cast this card for its miracle cost when you draw it if it's the first card you drew this turn.)

Octopus Umbra

Enchant creature
Enchanted creature has base power and toughness 8/8 and has "Whenever this creature attacks, you may tap target creature with power 8 or less."
Totem armor (If enchanted creature would be destroyed, instead remove all damage from it and destroy this Aura.)

Deep Spawn

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

Man-o'-War

When Man-o'-War enters the battlefield, return target creature to its owner's hand.

Wormfang Turtle

When Wormfang Turtle enters the battlefield, exile a land you control.
When Wormfang Turtle leaves the battlefield, return the exiled card to the battlefield under its owner's control.

Skyclave Squid

Defender
Landfall — Whenever a land enters the battlefield under your control, Skyclave Squid can attack this turn as though it didn't have defender.

Treasure Cruise

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Draw three cards.

Sea-Dasher Octopus

Mutate {1}{U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Flash
Whenever this creature deals combat damage to a player, draw a card.

King Crab

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

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice Mind Stone: Draw a card.

Walking Sponge

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

Read the Tides

Choose one —
• Draw three cards.
• Return up to two target creatures to their owners' hands.

Charix, the Raging Isle

Spells your opponents cast that target Charix, the Raging Isle cost {2} more to cast.
{3}: Charix gets +X/-X until end of turn, where X is the number of Islands you control.

Hedron Crab

Landfall — Whenever a land enters the battlefield under your control, target player mills three cards.

Riptide Turtle

Sigiled Starfish

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