Scattering Stroke

Counter target spell. Clash with an opponent. If you win, at the beginning of your next main phase, you may add an amount of {C} equal to that spell's mana value. (Each clashing player reveals the top card of their library, then puts that card on the top or bottom. A player wins if their card had a higher mana value.)

Engulf the Shore

Return to their owners' hands all creatures with toughness less than or equal to the number of Islands you control.

Scourge of Fleets

When Scourge of Fleets 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.

Lullmage Mentor

Whenever a spell or ability you control counters a spell, you may create a 1/1 blue Merfolk creature token.
Tap seven untapped Merfolk you control: Counter target spell.

Remote Isle

Remote Isle enters tapped.
{T}: Add {U}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Crush of Tentacles

Surge {3}{U}{U} (You may cast this spell for its surge cost if you or a teammate has cast another spell this turn.)
Return all nonland permanents to their owners' hands. If this spell's surge cost was paid, create an 8/8 blue Octopus creature token.

Kopala, Warden of Waves

Spells your opponents cast that target a Merfolk you control cost {2} more to cast.
Abilities your opponents activate that target a Merfolk you control cost {2} more to activate.

Wake Thrasher

Whenever a permanent you control becomes untapped, Wake Thrasher gets +1/+1 until end of turn.

Merrow Commerce

At the beginning of your end step, untap all Merfolk you control.

Drag Under

Return target creature to its owner's hand.
Draw a card.

Halimar Depths

Halimar Depths enters tapped.
When Halimar Depths enters, look at the top three cards of your library, then put them back in any order.
{T}: Add {U}.

Merrow Reejerey

Other Merfolk creatures you control get +1/+1.
Whenever you cast a Merfolk spell, you may tap or untap target permanent.

Rootwater Thief

{U}: Rootwater Thief gains flying until end of turn.
Whenever Rootwater Thief deals combat damage to a player, you may pay {2}. If you do, search that player's library for a card and exile it, then the player shuffles.

Talrand, Sky Summoner

Whenever you cast an instant or sorcery spell, create a 2/2 blue Drake creature token with flying.

Breaking Wave

You may cast Breaking Wave as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)
Simultaneously untap all tapped creatures and tap all untapped creatures.

Empress Galina

{U}{U}, {T}: Gain control of target legendary permanent. (This effect lasts indefinitely.)

Seafloor Oracle

Whenever a Merfolk you control deals combat damage to a player, draw a card.

Sea Scryer

Seasinger

When you control no Islands, sacrifice Seasinger.
You may choose not to untap Seasinger during your untap step.
{T}: Gain control of target creature whose controller controls an Island for as long as you control Seasinger and Seasinger remains tapped.

Stormtide Leviathan

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
All lands are Islands in addition to their other types.
Creatures without flying or islandwalk can't attack.

Crashing Tide

This spell has flash as long as you control a Merfolk.
Return target creature to its owner's hand.
Draw a card.

True-Name Nemesis

As True-Name Nemesis enters, choose a player.
True-Name Nemesis has protection from the chosen player.

River Sneak

River Sneak can't be blocked.
Whenever another Merfolk you control enters, River Sneak gets +1/+1 until end of turn.

Mistcaller

Sacrifice Mistcaller: Until end of turn, if a nontoken creature would enter and it wasn't cast, exile it instead.

Silent Submersible

Whenever Silent Submersible deals combat damage to a player or planeswalker, draw a card.
Crew 2 (Tap any number of creatures you control with total power 2 or more: This Vehicle becomes an artifact creature until end of turn.)

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Sapphire Medallion

Blue spells you cast cost {1} less to cast.

Riverwise Augur

When Riverwise Augur enters, draw three cards, then put two cards from your hand on top of your library in any order.

Flooded Shoreline

{U}{U}, Return two Islands you control to their owner's hand: Return target creature to its owner's hand.

Benthic Biomancer

{1}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on Benthic Biomancer, draw a card, then discard a card.

Aquatic Incursion

When Aquatic Incursion enters, create two 1/1 blue Merfolk creature tokens with hexproof. (They can't be the targets of spells or abilities your opponents control.)
{3}{U}: Target Merfolk can't be blocked this turn.

Thassa's Rebuff

Counter target spell unless its controller pays {X}, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Aquitect's Will

Put a flood counter on target land. That land is an Island in addition to its other types for as long as it has a flood counter on it. If you control a Merfolk, draw a card.

Vodalian War Machine

Defender (This creature can't attack.)
Tap an untapped Merfolk you control: Vodalian War Machine can attack this turn as though it didn't have defender.
Tap an untapped Merfolk you control: Vodalian War Machine gets +2/+1 until end of turn.
When Vodalian War Machine dies, destroy all Merfolk tapped this turn to pay for its abilities.

Whelming Wave

Return all creatures to their owners' hands except for Krakens, Leviathans, Octopuses, and Serpents.

Cursecatcher

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

Deepchannel Mentor

Blue creatures you control can't be blocked.

Thada Adel, Acquisitor

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever Thada Adel, Acquisitor deals combat damage to a player, search that player's library for an artifact card and exile it. Then that player shuffles. Until end of turn, you may play that card.

Merfolk Trickster

Flash
When Merfolk Trickster enters, tap target creature an opponent controls. It loses all abilities until end of turn.

Mutavault

{T}: Add {C}.
{1}: Mutavault becomes a 2/2 creature with all creature types until end of turn. It's still a land.

Expel from Orazca

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
Return target nonland permanent to its owner's hand. If you have the city's blessing, you may put that permanent on top of its owner's library instead.

Leyline of Anticipation

If Leyline of Anticipation is in your opening hand, you may begin the game with it on the battlefield.
You may cast spells as though they had flash.

Quicksilver Fountain

At the beginning of each player's upkeep, that player puts a flood counter on target non-Island land they control of their choice. That land is an Island for as long as it has a flood counter on it.
At the beginning of each end step, if all lands on the battlefield are Islands, remove all flood counters from them.

Tidebinder Mage

When Tidebinder Mage enters, tap target red or green creature an opponent controls. That creature doesn't untap during its controller's untap step for as long as you control Tidebinder Mage.

Lord of Atlantis

Other Merfolk get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Tempest Caller

When Tempest Caller enters, tap all creatures target opponent controls.

Vodalian Mage

{U}, {T}: Counter target spell unless its controller pays {1}.

Negate

River's Rebuke

Return all nonland permanents target player controls to their owner's hand.

Coralhelm Commander

Level up {1} ({1}: Put a level counter on this. Level up only as a sorcery.)
LEVEL 2-3
3/3
Flying
LEVEL 4+
4/4
Flying
Other Merfolk creatures you control get +1/+1.

Pongify

Destroy target creature. It can't be regenerated. Its controller creates a 3/3 green Ape creature token.

Kindred Discovery

As Kindred Discovery enters, choose a creature type.
Whenever a creature you control of the chosen type enters or attacks, draw a card.

Merfolk Wayfinder

Flying
When Merfolk Wayfinder enters, reveal the top three cards of your library. Put all Island cards revealed this way into your hand and the rest on the bottom of your library in any order.

Military Intelligence

Whenever you attack with two or more creatures, draw a card.

Gush

You may return two Islands you control to their owner's hand rather than pay this spell's mana cost.
Draw two cards.

Wanderwine Prophets

Champion a Merfolk (When this enters, sacrifice it unless you exile another Merfolk you control. When this leaves the battlefield, that card returns to the battlefield.)
Whenever Wanderwine Prophets deals combat damage to a player, you may sacrifice a Merfolk. If you do, take an extra turn after this one.

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Deeproot Waters

Whenever you cast a Merfolk spell, create a 1/1 blue Merfolk creature token with hexproof. (A creature with hexproof can't be the target of spells or abilities your opponents control.)

Merfolk Looter

Coastal Piracy

Whenever a creature you control deals combat damage to an opponent, you may draw a card.

Merrow Harbinger

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
When Merrow Harbinger enters, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.

Enclave Cryptologist

Level up {1}{U} ({1}{U}: Put a level counter on this. Level up only as a sorcery.)
LEVEL 1-2
0/1
{T}: Draw a card, then discard a card.
LEVEL 3+
0/1
{T}: Draw a card.

Overtaker

{3}{U}, {T}, Discard a card: Untap target creature and gain control of it until end of turn. That creature gains haste until end of turn.

Mist-Cloaked Herald

Tidal Bore

You may return an Island you control to its owner's hand rather than pay this spell's mana cost.
You may tap or untap target creature.

Merfolk Sovereign

Other Merfolk creatures you control get +1/+1.
{T}: Target Merfolk creature can't be blocked this turn.

Mind Spring

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.

Thassa, God of the Sea

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
At the beginning of your upkeep, scry 1.
{1}{U}: Target creature you control can't be blocked this turn.

Silvergill Adept

As an additional cost to cast this spell, reveal a Merfolk card from your hand or pay {3}.
When Silvergill Adept enters, draw a card.

Benthicore

When Benthicore enters, create two 1/1 blue Merfolk Wizard creature tokens.
Tap two untapped Merfolk you control: Untap Benthicore. It gains shroud until end of turn. (It can't be the target of spells or abilities.)

Master of Waves

Protection from red
Elemental creatures you control get +1/+1.
When Master of Waves enters, create a number of 1/0 blue Elemental creature tokens equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Inundate

Return all nonblue creatures to their owners' hands.

Spreading Seas

Enchant land
When Spreading Seas enters, draw a card.
Enchanted land is an Island.

Cosi's Trickster

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

Harbinger of the Tides

You may cast Harbinger of the Tides 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 Harbinger of the Tides enters, you may return target tapped creature an opponent controls to its owner's hand.

Sea's Claim

Enchant land (Target a land as you cast this. This card enters attached to that land.)
Enchanted land is an Island.

Familiar's Ruse

As an additional cost to cast this spell, return a creature you control to its owner's hand.
Counter target spell.

Foil

You may discard an Island card and another card rather than pay this spell's mana cost.
Counter target spell.

Seahunter

{3}, {T}: Search your library for a Merfolk permanent card, put it onto the battlefield, then shuffle.

High Tide

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

Coral Atoll

Coral Atoll enters tapped.
When Coral Atoll enters, sacrifice it unless you return an untapped Island you control to its owner's hand.
{T}: Add {C}{U}.

Lonely Sandbar

Lonely Sandbar enters tapped.
{T}: Add {U}.
Cycling {U} ({U}, Discard this card: Draw a card.)

Tidal Warrior

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

Master of the Pearl Trident

Other Merfolk creatures you control get +1/+1 and have islandwalk. (They can't be blocked as long as defending player controls an Island.)

Triton Tactics

Up to two target creatures each get +0/+3 until end of turn. Untap those creatures. At this turn's next end of combat, tap each creature that was blocked by one of those creatures this turn and it doesn't untap during its controller's next untap step.

Rapid Hybridization

Destroy target creature. It can't be regenerated. That creature's controller creates a 3/3 green Frog Lizard creature token.

Research the Deep

Draw a card. Clash with an opponent. If you win, return Research the Deep to its owner's hand. (Each clashing player reveals the top card of their library, then puts that card on the top or bottom. A player wins if their card had a higher mana value.)

Declaration of Naught

As Declaration of Naught enters, choose a card name.
{U}: Counter target spell with the chosen name.

Slinn Voda, the Rising Deep

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
When Slinn Voda, the Rising Deep enters, if it was kicked, return all creatures to their owners' hands except for Merfolk, Krakens, Leviathans, Octopuses, and Serpents.

Flow of Ideas

Wash Out

Return all permanents of the color of your choice to their owners' hands.

Lingering Mirage

Enchant land
Enchanted land is an Island.
Cycling {2} ({2}, Discard this card: Draw a card.)

Island

Stonybrook Banneret

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Merfolk spells and Wizard spells you cast cost {1} less to cast.

Surgespanner

Whenever Surgespanner becomes tapped, you may pay {1}{U}. If you do, return target permanent to its owner's hand.

Sigil Tracer

{1}{U}, Tap two untapped Wizards you control: Copy target instant or sorcery spell. You may choose new targets for the copy.

Herald of Secret Streams

Creatures you control with +1/+1 counters on them can't be blocked.

Reef Shaman

{T}: Target land becomes the basic land type of your choice until end of turn.

Tidal Courier

When Tidal Courier enters, reveal the top four cards of your library. Put all Merfolk cards revealed this way into your hand and the rest on the bottom of your library in any order.
{3}{U}: Tidal Courier gains flying until end of turn.