Cephalid Constable

Whenever this creature deals combat damage to a player, return up to that many target permanents that player controls to their owner's hand.

Waterwhirl

Return up to two target creatures to their owners' hands.

Aegis Turtle

Eluge, the Shoreless Sea

Eluge's power and toughness are each equal to the number of Islands you control.
Whenever Eluge enters or attacks, put a flood counter on target land. It's an Island in addition to its other types for as long as it has a flood counter on it.
The first instant or sorcery spell you cast each turn costs {U} (or {1}) less to cast for each land you control with a flood counter on it.

Caller of Gales

{1}{U}, {T}: Target creature gains flying until end of turn.

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.)

Glimmerbell

Sigiled Starfish

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

Ancient Crab

Evolving Wilds

{T}, Sacrifice this land: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Pond Prophet

Charix, the Raging Isle

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

Octoprophet

When this creature enters, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Bigfin Bouncer

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

Mystic Skyfish

Whenever you draw your second card each turn, this creature gains flying until end of turn.

Prairie Stream

({T}: Add {W} or {U}.)
This land enters tapped unless you control two or more basic lands.

Island

Commander's Sphere

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

Chulane, Teller of Tales

Vigilance
Whenever you cast a creature spell, draw a card, then you may put a land card from your hand onto the battlefield.
{3}, {T}: Return target creature you control to its owner's hand.

Stinging Lionfish

Whenever you cast your first spell during each opponent's turn, you may tap or untap target nonland permanent.

Canopy Vista

({T}: Add {G} or {W}.)
This land enters tapped unless you control two or more basic lands.

Seaside Citadel

This land enters tapped.
{T}: Add {G}, {W}, or {U}.

Bronze Walrus

When this creature enters, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)
{T}: Add one mana of any color.

Theoretical Duplication

Whenever a nontoken creature an opponent controls enters this turn, create a token that's a copy of that creature.

Phantasmal Shieldback

When this creature becomes the target of a spell or ability, sacrifice it.
When this creature dies, draw a card.

Terrarion

This artifact enters tapped.
{2}, {T}, Sacrifice this artifact: Add two mana in any combination of colors.
When this artifact is put into a graveyard from the battlefield, draw a card.

Dreamtide Whale

Vanishing 2 (This creature enters with two time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
Whenever a player casts their second spell each turn, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Quicksilver Fisher

Flying
When this creature enters, draw a card, then discard a card.

Deepglow Skate

When this creature enters, double the number of each kind of counter on any number of target permanents.

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Windrider Eel

Flying
Landfall — Whenever a land you control enters, this creature gets +2/+2 until end of turn.

Fishing Pole

Equipped creature has "{1}, {T}, Tap Fishing Pole: Put a bait counter on Fishing Pole."
Whenever equipped creature becomes untapped, remove a bait counter from this Equipment. If you do, create a 1/1 blue Fish creature token.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Tidal Barracuda

Any player may cast spells as though they had flash.
Your opponents can't cast spells during your turn.

Kraken's Eye

Whenever a player casts a blue spell, you may gain 1 life.

Aven Fisher

Flying (This creature can't be blocked except by creatures with flying or reach.)
When this creature dies, you may draw a card.

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.

Tidal Warrior

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

Purple-Crystal Crab

Decanter of Endless Water

You have no maximum hand size.
{T}: Add one mana of any color.

Spined Megalodon

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Whenever this creature attacks, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Water Wings

Until end of turn, target creature you control has base power and toughness 4/4 and gains flying and hexproof. (It can't be the target of spells or abilities your opponents control.)

Forest

Terramorphic Expanse

Kraken Hatchling

Vivid Flying Fish

This creature has flying as long as it's attacking. (It can't be blocked except by creatures with flying or reach.)

Sleep with the Fishes

Enchant creature
When this Aura enters, tap enchanted creature and you create a 1/1 blue Fish creature token with "This token can't be blocked."
Enchanted creature doesn't untap during its controller's untap step.

Fisher's Talent

(Gain the next level as a sorcery to add its ability.)
At the beginning of your upkeep, look at the top card of your library. You may reveal it if it's a land card. Create a 1/1 blue Fish creature token if you revealed it this way. Then draw a card.
{G}{U}: Level 2
If you would create a Fish token, create a 3/3 blue Shark creature token instead.
{2}{G}{U}: Level 3
If you would create a Shark token, create an 8/8 blue Octopus creature token instead.

Cephalid Inkmage

When this creature enters, surveil 3. (Look at the top three cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)
Threshold — This creature can't be blocked as long as there are seven or more cards in your graveyard.

Tranquil Landscape

{T}: Add {C}.
{T}, Sacrifice this land: Search your library for a basic Forest, Plains, or Island card, put it onto the battlefield tapped, then shuffle.
Cycling {G}{W}{U} ({G}{W}{U}, Discard this card: Draw a card.)

Azorius Signet

Lifecrafter's Bestiary

At the beginning of your upkeep, scry 1.
Whenever you cast a creature spell, you may pay {G}. If you do, draw a card.

Simic Growth Chamber

This land enters tapped.
When this land enters, return a land you control to its owner's hand.
{T}: Add {G}{U}.

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Hydroid Krasis

When you cast this spell, you gain half X life and draw half X cards. Round down each time.
Flying, trample
This creature enters with X +1/+1 counters on it.

Thought Vessel

Arcane Signet

Sol Ring

Hardened Scales

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

Daggermaw Megalodon

Vigilance
Islandcycling {2} ({2}, Discard this card: Search your library for an Island card, reveal it, put it into your hand, then shuffle.)

Man-o'-War

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

Plains

Part the Waterveil

Take an extra turn after this one. Exile Part the Waterveil.
Awaken 6—{6}{U}{U}{U} (If you cast this spell for {6}{U}{U}{U}, also put six +1/+1 counters on target land you control and it becomes a 0/0 Elemental creature with haste. It's still a land.)

Wavebreak Hippocamp

Whenever you cast your first spell during each opponent's turn, draw a card.

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.

Manta Riders

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

Harbinger of the Tides

You may cast this card as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)
When this creature enters, you may return target tapped creature an opponent controls to its owner's hand.

Phase Dolphin

Whenever this creature attacks, another target attacking creature can't be blocked this turn.

Cold-Water Snapper

Hexproof (This creature can't be the target of spells or abilities your opponents control.)

Ichthyomorphosis

Enchant creature
Enchanted creature loses all abilities and is a blue Fish with base power and toughness 0/1.

Cloud Manta

Fleet Swallower

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

Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Unruly Krasis

Trample
Whenever this creature attacks, you may have the base power and toughness of another target creature you control become X/X until end of turn, where X is this creature's power.
{3}{G}{U}: Adapt 3. (If this creature has no +1/+1 counters on it, put three +1/+1 counters on it.)

Exotic Pets

Create two 1/1 blue Fish creature tokens with "This token can't be blocked." Then for each kind of counter among creatures you control, put a counter of that kind on either of those tokens.

Lifecrafter's Gift

Put a +1/+1 counter on target creature, then put a +1/+1 counter on each creature you control with a +1/+1 counter on it.