Merfolk Trickster

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

Terramorphic Expanse

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

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.

Evolving Wilds

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

Propaganda

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Wake Thrasher

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

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.

Rivendell

Rivendell enters tapped unless you control a legendary creature.
{T}: Add {U}.
{1}{U}, {T}: Scry 2. Activate only if you control a legendary creature.

Seafloor Oracle

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

Merfolk Sovereign

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

Deepchannel Mentor

Blue creatures you control can't be blocked.

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.)

Merrow Commerce

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

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.

Chart a Course

Draw two cards. Then discard a card unless you attacked this turn.

Dramatic Reversal

Untap all nonland permanents you control.

Reconnaissance Mission

Whenever a creature you control deals combat damage to a player, you may draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

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.

Coralhelm Chronicler

Whenever you cast a kicked spell, draw a card, then discard a card.
When Coralhelm Chronicler enters, look at the top five cards of your library. You may reveal a card with a kicker ability from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Political Trickery

Exchange control of target land you control and target land an opponent controls. (This effect lasts indefinitely.)

Aetherize

Return all attacking creatures to their owner's hand.

Patchwork Banner

As Patchwork Banner enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
{T}: Add one mana of any color.

Merrow Reejerey

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

River Sneak

River Sneak can't be blocked.
Whenever another Merfolk you control enters, River Sneak gets +1/+1 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.)

Lonely Sandbar

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

Kefnet's Monument

Blue creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, target creature an opponent controls doesn't untap during its controller's next untap step.

Mist-Cloaked Herald

Sol Ring

Counterspell

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.

Arcane Signet

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

Svyelun of Sea and Sky

Svyelun of Sea and Sky has indestructible as long as you control at least two other Merfolk.
Whenever Svyelun attacks, draw a card.
Other Merfolk you control have ward {1}. (Whenever another Merfolk you control becomes the target of a spell or ability an opponent controls, counter it unless that player pays {1}.)

Path of Ancestry

Path of Ancestry enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Military Intelligence

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

Skullclamp

Equipped creature gets +1/-1.
Whenever equipped creature dies, draw two cards.
Equip {1}

Reflections of Littjara

As Reflections of Littjara enters, choose a creature type.
Whenever you cast a spell of the chosen type, copy that spell. (A copy of a permanent spell becomes a token.)

Merfolk Windrobber

Flying
Whenever Merfolk Windrobber deals combat damage to a player, that player mills a card. (They put the top card of their library into their graveyard.)
Sacrifice Merfolk Windrobber: Draw a card. Activate only if an opponent has eight or more cards in their graveyard.

Decanter of Endless Water

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

Defiler of Dreams

Flying
As an additional cost to cast blue permanent spells, you may pay 2 life. Those spells cost {U} less to cast if you paid life this way. This effect reduces only the amount of blue mana you pay.
Whenever you cast a blue permanent spell, draw a card.

Deeproot Pilgrimage

Whenever one or more nontoken Merfolk you control become tapped, create a 1/1 blue Merfolk creature token with hexproof.

Mystic Sanctuary

({T}: Add {U}.)
Mystic Sanctuary enters tapped unless you control three or more other Islands.
When Mystic Sanctuary enters untapped, you may put target instant or sorcery card from your graveyard on top of your library.

Rishadan Dockhand

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
{1}, {T}: Tap target land.

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.)

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.

Lord of Atlantis

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

Engulf the Shore

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

Negate

Ponder

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

Back to Basics

Nonbasic lands don't untap during their controllers' untap steps.

Harbinger of the Seas

Distant Melody

Choose a creature type. Draw a card for each permanent you control of that type.

Inkwell Leviathan

Trample
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Shroud (This creature can't be the target of spells or abilities.)

Cosi's Trickster

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

Sapphire Medallion

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

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.

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 Hexcatcher

Flash
Other Merfolk you control get +1/+1.
Sacrifice a Merfolk: Counter target noncreature spell unless its controller pays {1}.

Command Tower

Reliquary Tower

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

Tempest Caller

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

Thieving Skydiver

Kicker {X}. X can't be 0. (You may pay an additional {X} as you cast this spell.)
Flying
When Thieving Skydiver enters, if it was kicked, gain control of target artifact with mana value X or less. If that artifact is an Equipment, attach it to Thieving Skydiver.

Triton Shorestalker

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.

Castle Vantress

Castle Vantress enters tapped unless you control an Island.
{T}: Add {U}.
{2}{U}{U}, {T}: Scry 2.

Spectral Deluge

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.
Foretell {1}{U}{U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Rogue's Passage

{T}: Add {C}.
{4}, {T}: Target creature can't be blocked this turn.

High Tide

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

Adaptive Automaton

As this creature enters, choose a creature type.
This creature is the chosen type in addition to its other types.
Other creatures you control of the chosen type get +1/+1.

Mist Dancer

Flying
Other Merfolk you control get +1/+0 and have flying.
Encore {5}{U}{U} ({5}{U}{U}, Exile this card from your graveyard: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)

Merfolk Spy

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever Merfolk Spy deals combat damage to a player, that player reveals a card at random from their hand.

Sky Diamond

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Island

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.