Killer Whale

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

Thoughtbind

Counter target spell with mana value 4 or less.

Cold-Water Snapper

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

Brinelin, the Moon Kraken

When Brinelin enters and whenever you cast a spell with mana value 6 or greater, you may return target nonland permanent to its owner's hand.
Partner (You can have two commanders if both have partner.)

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.

Armored Cancrix

Scrapdiver Serpent

This creature can't be blocked as long as defending player controls an artifact.

Rootwater Commando

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

Negate

Kefnet's Last Word

Gain control of target artifact, creature, or enchantment. Lands you control don't untap during your next untap step.

Skyswimmer Koi

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

Horseshoe Crab

Thriving Turtle

When this creature enters, you get {E}{E} (two energy counters).
Whenever this creature attacks, you may pay {E}{E}. If you do, put a +1/+1 counter on it.

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.

Shimmering Wings

Enchant creature (Target a creature as you cast this. This card enters attached to that creature.)
Enchanted creature has flying. (It can't be blocked except by creatures with flying or reach.)
{U}: Return this Aura to its owner's hand.

Capsizing Wave

Return target creature to its owner's hand. (Then exile this card. You may cast the creature later from exile.)

Sword Coast Serpent

This creature can't be blocked as long as you've cast a noncreature spell this turn.

Sword Coast Serpent // Capsizing Wave

Dispel

Kraken Hatchling

Sailors' Bane

This spell costs {1} less to cast for each card you own in exile and in your graveyard that's an instant card, a sorcery card, or a card that has an Adventure.
Ward {4} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {4}.)

Divination

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.

Aegis Turtle

Essence Scatter

Crystacean

Flash (You may cast this spell any time you could cast an instant.)

Dissolve

Counter target spell. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

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.

Phase Dolphin

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

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Wavebreak Hippocamp

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

Turn Aside

Counter target spell that targets a permanent you control.

Annul

Counter target artifact or enchantment spell.

Sol Ring

Mulldrifter

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

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.

Sky Diamond

This artifact enters tapped.
{T}: Add {U}.

Bind the Monster

Enchant creature
When this Aura enters, tap enchanted creature. It deals damage to you equal to its power.
Enchanted creature doesn't untap during its controller's untap step.

Metallic Rebuke

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)
Counter target spell unless its controller pays {3}.

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.

Spell Snuff

Counter target spell.
Fateful hour — If you have 5 or less life, draw a card.

Mirrorshell Crab

Ward {3} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {3}.)
Channel — {2}{U}, Discard this card: Counter target spell or ability unless its controller pays {3}.

Disdainful Stroke

Counter target spell with mana value 4 or greater.

Kheru Spellsnatcher

Morph {4}{U}{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 this creature is turned face up, counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard. You may cast that card without paying its mana cost for as long as it remains exiled.

Moat Piranhas

Stinging Lionfish

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

Shipwreck Moray

When this creature enters, you get {E}{E}{E}{E} (four energy counters).
Pay {E}: This creature gets +2/-2 until end of turn.

Shoal Serpent

Defender
Landfall — Whenever a land you control enters, this creature loses defender until end of turn.

Island

Diamond Mare

As this creature enters, choose a color.
Whenever you cast a spell of the chosen color, you gain 1 life.

Reservoir Kraken

Trample, ward {2}
At the beginning of each combat, if this creature is untapped, any opponent may tap an untapped creature they control. If they do, tap this creature and create a 1/1 blue Fish creature token with "This token can't be blocked."

Wayfarer's Bauble

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

Kasmina, Enigmatic Mentor

Spells your opponents cast that target a creature or planeswalker you control cost {2} more to cast.
−2: Create a 2/2 blue Wizard creature token. Draw a card, then discard a card.

Witness Protection

Enchant creature
Enchanted creature loses all abilities and is a green and white Citizen creature with base power and toughness 1/1 named Legitimate Businessperson. (It loses all other colors, card types, creature types, and names.)

Cancel

Remove Soul

Cloaked Siren

Flash (You may cast this spell any time you could cast an instant.)
Flying

Armillary Sphere

{2}, {T}, Sacrifice this artifact: Search your library for up to two basic land cards, reveal them, put them into your hand, then shuffle.

Giant Tortoise

This creature gets +0/+3 as long as it's untapped.

Syphon Essence

Counter target creature or planeswalker spell. Create a Blood token. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this token: Draw a card.")

Hightide Hermit

Defender
When this creature enters, you get {E}{E}{E}{E} (four energy counters).
Pay {E}{E}: This creature can attack this turn as though it didn't have defender.

Convolute

Counter target spell unless its controller pays {4}.

You See a Guard Approach

Choose one —
• Distract the Guard — Tap target creature.
• Hide — Target creature you control gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)

Serpent of the Endless Sea

Serpent of the Endless Sea's power and toughness are each equal to the number of Islands you control.
This creature can't attack unless defending player controls an Island.

Prohibit

Kicker {2} (You may pay an additional {2} as you cast this spell.)
Counter target spell if its mana value is 2 or less. If this spell was kicked, counter that spell if its mana value is 4 or less instead.

Mana Chains

Enchant creature
Enchanted creature has "Cumulative upkeep {1}." (At the beginning of its controller's upkeep, that player puts an age counter on it, then sacrifices it unless they pay its upkeep cost for each age counter on it.)