Benthic Behemoth

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

Cloudkin Seer

Flying
When Cloudkin Seer enters the battlefield, draw a card.

Deepglow Skate

When Deepglow Skate enters the battlefield, double the number of each kind of counter on any number of target permanents.

Expedition Diviner

Flying
As long as you control another Wizard, Expedition Diviner has "When this creature dies, draw a card."

Animar, Soul of Elements

Protection from white and from black
Whenever you cast a creature spell, put a +1/+1 counter on Animar, Soul of Elements.
Creature spells you cast cost {1} less to cast for each +1/+1 counter on Animar.

Elusive Krasis

Elusive Krasis can't be blocked.
Evolve (Whenever a creature enters the battlefield under your control, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Fallowsage

Whenever Fallowsage becomes tapped, you may draw a card.

Brineborn Cutthroat

Flash (You may cast this spell any time you could cast an instant.)
Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on Brineborn Cutthroat.

Clinging Anemones

Defender
Evolve (Whenever a creature enters the battlefield under your control, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Esperzoa

Flying
At the beginning of your upkeep, return an artifact you control to its owner's hand.

Bounding Krasis

Flash (You may cast this spell any time you could cast an instant.)
When Bounding Krasis enters the battlefield, you may tap or untap target creature.

Chasm Skulker

Whenever you draw a card, put a +1/+1 counter on Chasm Skulker.
When Chasm Skulker dies, create X 1/1 blue Squid creature tokens with islandwalk, where X is the number of +1/+1 counters on Chasm Skulker. (They can't be blocked as long as defending player controls an Island.)

Colossal Whale

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

Daring Saboteur

{2}{U}: Daring Saboteur can't be blocked this turn.
Whenever Daring Saboteur deals combat damage to a player, you may draw a card. If you do, discard a card.

Aeromoeba

Flying
Discard a card: Switch Aeromoeba's power and toughness until end of turn.

Eon Frolicker

Flying
When Eon Frolicker enters the battlefield, if you cast it, target opponent takes an extra turn after this one. Until your next turn, you and planeswalkers you control gain protection from that player. (You and planeswalkers you control can't be targeted, dealt damage, or enchanted by anything controlled by that player.)

Augur of Bolas

When Augur of Bolas enters the battlefield, look at the top three cards of your library. You may reveal an instant or sorcery card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Cosi's Trickster

Whenever an opponent shuffles their library, you may put a +1/+1 counter on Cosi's Trickster.

Fortress Crab

Cryptic Serpent

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.

Cloud Manta

Coral Commando

Frilled Sea Serpent

{5}{U}{U}: Frilled Sea Serpent can't be blocked this turn.

Archipelagore

Mutate {5}{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.)
Whenever this creature mutates, tap up to X target creatures, where X is the number of times this creature has mutated. Those creatures don't untap during their controller's next untap step.

Emperor Mihail II

You may look at the top card of your library any time.
You may cast Merfolk spells from the top of your library.
Whenever you cast a Merfolk spell, you may pay {1}. If you do, create a 1/1 blue Merfolk creature token.

Giant Tortoise

Giant Tortoise gets +0/+3 as long as it's untapped.

Glimmerbell

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.

Aegis Turtle

Fleet Swallower

Whenever Fleet Swallower attacks, target player mills half their library, rounded up.

Caller of Gales

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

Cavalier of Gales

Flying
When Cavalier of Gales enters the battlefield, draw three cards, then put two cards from your hand on top of your library in any order.
When Cavalier of Gales dies, shuffle it into its owner's library, then scry 2.

Cold-Water Snapper

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

Glacial Crasher

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Glacial Crasher can't attack unless there is a Mountain on the battlefield.

Dakra Mystic

{U}, {T}: Each player reveals the top card of their library. You may put the revealed cards into their owners' graveyards. If you don't, each player draws a card.

Arixmethes, Slumbering Isle

Arixmethes, Slumbering Isle enters the battlefield tapped with five slumber counters on it.
As long as Arixmethes has a slumber counter on it, it's a land. (It's not a creature.)
Whenever you cast a spell, you may remove a slumber counter from Arixmethes.
{T}: Add {G}{U}.

Deep-Sea Terror

Deep-Sea Terror can't attack unless there are seven or more cards in your graveyard.

Breaching Hippocamp

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

Cursecatcher

Sacrifice Cursecatcher: Counter target instant or sorcery spell unless its controller pays {1}.

Armored Whirl Turtle

Drowner Initiate

Whenever a player casts a blue spell, you may pay {1}. If you do, target player mills two cards.