Jace's Mindseeker

Flying
When this creature enters, target opponent mills five cards. You may cast an instant or sorcery spell from among them without paying its mana cost.

Skitter Eel

{2}{U}: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)

Piranha Fly

Ancient Carp

Dandân

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

Cloud Manta

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.

Kapsho Kitefins

Flying
Whenever this creature or another creature you control enters, tap target creature an opponent controls.

Bubble Smuggler

Disguise {5}{U} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.)
As this creature is turned face up, put four +1/+1 counters on it.

Scrounging Skyray

Flying
Whenever you discard one or more cards, put that many +1/+1 counters on this creature.
Cycling {2} ({2}, Discard this card: Draw a card.)

Slipstream Eel

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

Tui and La, Moon and Ocean

Whenever Tui and La become tapped, draw a card.
Whenever Tui and La become untapped, put a +1/+1 counter on them.

Wavebreak Hippocamp

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

Moat Piranhas

Grisly Anglerfish

{6}: Creatures your opponents control attack this turn if able.

Grizzled Angler

{T}: Mill two cards. Then if there is a colorless creature card in your graveyard, transform this creature. (To mill two cards, put the top two cards of your library into your graveyard.)

Grizzled Angler // Grisly Anglerfish

Devouring Deep

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

Deepglow Skate

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

Giant Koi

Waterbend {3}: This creature can't be blocked this turn. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)
Islandcycling {2} ({2}, Discard this card: Search your library for an Island card, reveal it, put it into your hand, then shuffle.)

Flying Dolphin-Fish

Flying (This creature can't be blocked except by creatures with flying or reach.)

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.

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.)

Wormfang Behemoth

When this creature enters, exile all cards from your hand.
When this creature leaves the battlefield, return the exiled cards to their owner's hand.

Wormfang Manta

Flying
When this creature enters, you skip your next turn.
When this creature leaves the battlefield, you take an extra turn after this one.

Tidal Barracuda

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

Surge Mare

This creature can't be blocked by green creatures.
Whenever this creature deals damage to an opponent, you may draw a card. If you do, discard a card.
{1}{U}: This creature gets +2/-2 until end of turn.

Mystic Skyfish

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

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.

Windrider Eel

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

Coral Eel

Breaching Hippocamp

Flash (You may cast this spell any time you could cast an instant.)
When this creature enters, untap another target creature you control.

Skyswimmer Koi

Flying
Whenever an artifact you control enters, you may draw a card. If you do, discard a card.

Sky-Eel School

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

Fleet Swallower

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

Aboleth Spawn

Flash
Ward {2}
Probing Telepathy — Whenever a creature entering under an opponent's control causes a triggered ability of that creature to trigger, you may copy that ability. You may choose new targets for the copy.

Stinging Lionfish

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