Tideshaper Mystic

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

Mist-Cloaked Herald

Nahiri, the Lithomancer

+2: Create a 1/1 white Kor Soldier creature token. You may attach an Equipment you control to it.
−2: You may put an Equipment card from your hand or graveyard onto the battlefield.
−10: Create a colorless Equipment artifact token named Stoneforged Blade. It has indestructible, "Equipped creature gets +5/+5 and has double strike," and equip {0}.
Nahiri, the Lithomancer can be your commander.

Arcane Denial

Counter target spell. Its controller may draw up to two cards at the beginning of the next turn's upkeep.
You draw a card at the beginning of the next turn's upkeep.

Boompile

{T}: Flip a coin. If you win the flip, destroy all nonland permanents.

Dispel

Esper Sentinel

Whenever an opponent casts their first noncreature spell each turn, draw a card unless that player pays {X}, where X is Esper Sentinel's power.

High Tide

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

Skullclamp

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

Merfolk Pupil

When Merfolk Pupil enters the battlefield, draw a card, then discard a card.
{1}{U}, Exile Merfolk Pupil from your graveyard: Draw a card, then discard a card.

Worldslayer

Whenever equipped creature deals combat damage to a player, destroy all permanents other than Worldslayer.
Equip {5} ({5}: Attach to target creature you control. Equip only as a sorcery.)

Ironclad Slayer

When Ironclad Slayer enters the battlefield, you may return target Aura or Equipment card from your graveyard to your hand.

Merrow Commerce

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

Tempest Caller

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

Glacial Fortress

Glacial Fortress enters the battlefield tapped unless you control a Plains or an Island.
{T}: Add {W} or {U}.

Arcane Signet

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

Sword of the Animist

Equipped creature gets +1/+1.
Whenever equipped creature attacks, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Equip {2}

Wanderwine Hub

As Wanderwine Hub enters the battlefield, you may reveal a Merfolk card from your hand. If you don't, Wanderwine Hub enters the battlefield tapped.
{T}: Add {W} or {U}.

Mox Amber

{T}: Add one mana of any color among legendary creatures and planeswalkers you control.

Chromatic Lantern

Lands you control have "{T}: Add one mana of any color."
{T}: Add one mana of any color.

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.

Irrigated Farmland

({T}: Add {W} or {U}.)
Irrigated Farmland enters the battlefield tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

Thought Vessel

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

Sol Ring

Glacial Floodplain

({T}: Add {W} or {U}.)
Glacial Floodplain enters the battlefield tapped.

Whirlpool Rider

When Whirlpool Rider enters the battlefield, shuffle the cards from your hand into your library, then draw that many cards.

Island

Prairie Stream

({T}: Add {W} or {U}.)
Prairie Stream enters the battlefield tapped unless you control two or more basic lands.

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.

Ardenn, Intrepid Archaeologist

At the beginning of combat on your turn, you may attach any number of Auras and Equipment you control to target permanent or player.
Partner (You can have two commanders if both have partner.)

Sword of Sinew and Steel

Equipped creature gets +2/+2 and has protection from black and from red.
Whenever equipped creature deals combat damage to a player, destroy up to one target planeswalker and up to one target artifact.
Equip {2}

Coral Atoll

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

Citadel Gate

Citadel Gate enters the battlefield tapped.
As Citadel Gate enters the battlefield, choose a color other than white.
{T}: Add {W} or one mana of the chosen color.

Negate

Ponder

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

Tidal Courier

When Tidal Courier enters the battlefield, 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.

Tidal Visionary

{T}: Target creature becomes the color of your choice until end of turn.

Merfolk Sovereign

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

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.

Rootwater Diver

{T}, Sacrifice Rootwater Diver: Return target artifact card from your graveyard to your hand.

True-Name Nemesis

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

Azorius Signet

Tide Shaper

Kicker {1} (You may pay an additional {1} as you cast this spell.)
When Tide Shaper enters the battlefield, if it was kicked, target land becomes an Island for as long as Tide Shaper remains on the battlefield.
Tide Shaper gets +1/+1 as long as an opponent controls an Island.

Hammer of Nazahn

Whenever Hammer of Nazahn or another Equipment enters the battlefield under your control, you may attach that Equipment to target creature you control.
Equipped creature gets +2/+0 and has indestructible.
Equip {4}

Deadeye Quartermaster

When Deadeye Quartermaster enters the battlefield, you may search your library for an Equipment or Vehicle card, reveal it, put it into your hand, then shuffle.

Path of Ancestry

Path of Ancestry enters the battlefield 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.)

Open the Armory

Search your library for an Aura or Equipment card, reveal it, put it into your hand, then shuffle.

Decanter of Endless Water

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

Seafloor Oracle

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

Mistveil Plains

({T}: Add {W}.)
Mistveil Plains enters the battlefield tapped.
{W}, {T}: Put target card from your graveyard on the bottom of your library. Activate only if you control two or more white permanents.

Sigarda's Aid

You may cast Aura and Equipment spells as though they had flash.
Whenever an Equipment enters the battlefield under your control, you may attach it to target creature you control.

Triton Shorestalker

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}.)

Supreme Verdict

This spell can't be countered.
Destroy all creatures.

Bane's Contingency

Counter target spell. If that spell targets a commander you control, instead counter that spell, scry 2, then draw a card.

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.

Raving Visionary

{U}, {T}: Draw a card, then discard a card.
Delirium — {2}{U}, {T}: Draw a card. Activate only if there are four or more card types among cards in your graveyard.

Sword of Hearth and Home

Equipped creature gets +2/+2 and has protection from green and from white.
Whenever equipped creature deals combat damage to a player, exile up to one target creature you own, then search your library for a basic land card. Put both cards onto the battlefield under your control, then shuffle.
Equip {2}

Fortified Beachhead

As Fortified Beachhead enters the battlefield, you may reveal a Soldier card from your hand. Fortified Beachhead enters the battlefield tapped unless you revealed a Soldier card this way or you control a Soldier.
{T}: Add {W} or {U}.
{5}, {T}: Soldiers you control get +1/+1 until end of turn.

Talisman of Progress

{T}: Add {C}.
{T}: Add {W} or {U}. Talisman of Progress deals 1 damage to you.

Stoneforge Mystic

When Stoneforge Mystic enters the battlefield, you may search your library for an Equipment card, reveal it, put it into your hand, then shuffle.
{1}{W}, {T}: You may put an Equipment card from your hand onto the battlefield.

Stonybrook Angler

{1}{U}, {T}: You may tap or untap target creature.

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.

Mother of Runes

{T}: Target creature you control gains protection from the color of your choice until end of turn.

Brass Squire

{T}: Attach target Equipment you control to target creature you control.

Lord of Atlantis

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

Plains

Saprazzan Heir

Whenever Saprazzan Heir becomes blocked, you may draw three cards.

Relic Seeker

Renown 1 (When this creature deals combat damage to a player, if it isn't renowned, put a +1/+1 counter on it and it becomes renowned.)
When Relic Seeker becomes renowned, you may search your library for an Equipment card, reveal it, put it into your hand, then shuffle.

Flow of Knowledge

Draw a card for each Island you control, then discard two cards.

Dovin's Veto

This spell can't be countered.
Counter target noncreature spell.

Sygg, River Guide

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
{1}{W}: Target Merfolk you control gains protection from the color of your choice until end of turn.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Mantle of the Ancients

Enchant creature you control
When Mantle of the Ancients enters the battlefield, return any number of target Aura and/or Equipment cards from your graveyard to the battlefield attached to enchanted creature.
Enchanted creature gets +1/+1 for each Aura and Equipment attached to it.

Merfolk Looter

Soothsayer Adept

{1}{U}, {T}: Draw a card, then discard a card.

Vodalian Hexcatcher

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

Treasure Cruise

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Draw three cards.

Austere Command

Choose two —
• Destroy all artifacts.
• Destroy all enchantments.
• Destroy all creatures with mana value 3 or less.
• Destroy all creatures with mana value 4 or greater.

Merrow Reejerey

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

Steelshaper's Gift

Search your library for an Equipment card, reveal that card, put it into your hand, then shuffle.

Preordain

Scry 2, then draw a card. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Kindred Discovery

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

Idyllic Beachfront

({T}: Add {W} or {U}.)
Idyllic Beachfront enters the battlefield tapped.

Swan Song

Counter target enchantment, instant, or sorcery spell. Its controller creates a 2/2 blue Bird creature token with flying.

River Sneak

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

Merfolk Trickster

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

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.

Port Town

As Port Town enters the battlefield, you may reveal a Plains or Island card from your hand. If you don't, Port Town enters the battlefield tapped.
{T}: Add {W} or {U}.

Quest for the Holy Relic

Whenever you cast a creature spell, you may put a quest counter on Quest for the Holy Relic.
Remove five quest counters from Quest for the Holy Relic and sacrifice it: Search your library for an Equipment card, put it onto the battlefield, attach it to a creature you control, then shuffle.

Brainstorm

Draw three cards, then put two cards from your hand on top of your library in any order.

Nimbus Maze

{T}: Add {C}.
{T}: Add {W}. Activate only if you control an Island.
{T}: Add {U}. Activate only if you control a Plains.

Spreading Seas

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