Sol Ring

Temple of the False God

{T}: Add {C}{C}. Activate only if you control five or more lands.

Brainstorm

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

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.

Merfolk Trickster

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

Dig Through Time

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Look at the top seven cards of your library. Put two of them into your hand and the rest on the bottom of your library in any order.

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.

Zegana, Utopian Speaker

When Zegana, Utopian Speaker enters the battlefield, if you control another creature with a +1/+1 counter on it, draw a card.
{4}{G}{U}: Adapt 4. (If this creature has no +1/+1 counters on it, put four +1/+1 counters on it.)
Each creature you control with a +1/+1 counter on it has trample.

Arcane Signet

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

Simic Ascendancy

{1}{G}{U}: Put a +1/+1 counter on target creature you control.
Whenever one or more +1/+1 counters are put on a creature you control, put that many growth counters on Simic Ascendancy.
At the beginning of your upkeep, if Simic Ascendancy has twenty or more growth counters on it, you win the game.

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.

Nature's Claim

Destroy target artifact or enchantment. Its controller gains 4 life.

Merrow Reejerey

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

Seafloor Oracle

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

Herald of Secret Streams

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

Kiora, Master of the Depths

+1: Untap up to one target creature and up to one target land.
−2: Reveal the top four cards of your library. You may put a creature card and/or a land card from among them into your hand. Put the rest into your graveyard.
−8: You get an emblem with "Whenever a creature enters the battlefield under your control, you may have it fight target creature." Then create three 8/8 blue Octopus creature tokens.

Quandrix Campus

Quandrix Campus enters the battlefield tapped.
{T}: Add {G} or {U}.
{4}, {T}: Scry 1.

Island

Simic Signet

Unclaimed Territory

As Unclaimed Territory enters the battlefield, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type.

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.

Forerunner of the Heralds

When Forerunner of the Heralds enters the battlefield, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.
Whenever another Merfolk enters the battlefield under your control, put a +1/+1 counter on Forerunner of the Heralds.

Deeproot Wayfinder

Whenever Deeproot Wayfinder deals combat damage to a player or battle, surveil 1, then you may return a land card from your graveyard to the battlefield tapped. (To surveil 1, look at the top card of your library. You may put that card into your graveyard.)

Aetherize

Return all attacking creatures to their owner's hand.

Thornwood Falls

Thornwood Falls enters the battlefield tapped.
When Thornwood Falls enters the battlefield, you gain 1 life.
{T}: Add {G} or {U}.

Negate

Merfolk Sovereign

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

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.

Metallic Mimic

As Metallic Mimic enters the battlefield, choose a creature type.
Metallic Mimic is the chosen type in addition to its other types.
Each other creature you control of the chosen type enters the battlefield with an additional +1/+1 counter on it.

Talisman of Curiosity

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

Crawling Barrens

{T}: Add {C}.
{4}: Put two +1/+1 counters on Crawling Barrens. Then you may have it become a 0/0 Elemental creature until end of turn. It's still a land.

Merfolk Mistbinder

Evolving Wilds

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

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.)

Counterspell

Tishana, Voice of Thunder

Tishana, Voice of Thunder's power and toughness are each equal to the number of cards in your hand.
You have no maximum hand size.
When Tishana enters the battlefield, draw a card for each creature you control.

Swift Warden

Flash
When Swift Warden enters the battlefield, target Merfolk you control gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)

Mosswort Bridge

Hideaway 4 (When this land enters the battlefield, look at the top four cards of your library, exile one face down, then put the rest on the bottom in a random order.)
Mosswort Bridge enters the battlefield tapped.
{T}: Add {G}.
{G}, {T}: You may play the exiled card without paying its mana cost if creatures you control have total power 10 or greater.

Blackblade Reforged

Equipped creature gets +1/+1 for each land you control.
Equip legendary creature {3}
Equip {7}

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 the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

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.

Novijen, Heart of Progress

{T}: Add {C}.
{G}{U}, {T}: Put a +1/+1 counter on each creature that entered the battlefield this turn.

Vanquisher's Banner

As Vanquisher's Banner enters the battlefield, choose a creature type.
Creatures you control of the chosen type get +1/+1.
Whenever you cast a creature spell of the chosen type, draw a card.

Deeproot Champion

Whenever you cast a noncreature spell, put a +1/+1 counter on Deeproot Champion.

Tempest Caller

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

Cosi's Trickster

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

Merrow Harbinger

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

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.

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.

Kumena, Tyrant of Orazca

Tap another untapped Merfolk you control: Kumena, Tyrant of Orazca can't be blocked this turn.
Tap three untapped Merfolk you control: Draw a card.
Tap five untapped Merfolk you control: Put a +1/+1 counter on each Merfolk you control.

Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Surgespanner

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

Merfolk Skydiver

Flying
When Merfolk Skydiver enters the battlefield, put a +1/+1 counter on target creature you control.
{3}{G}{U}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Kodama's Reach

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Yavimaya Coast

{T}: Add {C}.
{T}: Add {G} or {U}. Yavimaya Coast deals 1 damage to you.

Command Tower

Murkfiend Liege

Other green creatures you control get +1/+1.
Other blue creatures you control get +1/+1.
Untap all green and/or blue creatures you control during each other player's untap step.

Temple of Mystery

Temple of Mystery enters the battlefield tapped.
When Temple of Mystery enters the battlefield, scry 1.
{T}: Add {G} or {U}.

Sigil Tracer

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

River's Rebuke

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

Guildmages' Forum

{T}: Add {C}.
{1}, {T}: Add one mana of any color. If that mana is spent on a multicolored creature spell, that creature enters the battlefield with an additional +1/+1 counter on it.

Winged Temple of Orazca

(Transforms from Hadana's Climb.)
{T}: Add one mana of any color.
{1}{G}{U}, {T}: Target creature you control gains flying and gets +X/+X until end of turn, where X is its power.

Hadana's Climb

At the beginning of combat on your turn, put a +1/+1 counter on target creature you control. Then if that creature has three or more +1/+1 counters on it, transform Hadana's Climb.

Hadana's Climb // Winged Temple of Orazca

Vodalian Hexcatcher

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

Seahunter

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

Cauldron of Souls

{T}: Choose any number of target creatures. Each of those creatures gains persist until end of turn. (When it dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Curse of the Swine

Exile X target creatures. For each creature exiled this way, its controller creates a 2/2 green Boar creature token.

Cold-Eyed Selkie

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever Cold-Eyed Selkie deals combat damage to a player, you may draw that many cards.

Forest

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.

Skullclamp

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

Seedborn Muse

Untap all permanents you control during each other player's untap step.

Cultivate

Merrow Commerce

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

Tatyova, Benthic Druid

Landfall — Whenever a land enters the battlefield under your control, you gain 1 life and draw a card.

Fallowsage

Whenever Fallowsage becomes tapped, you may draw a card.

Benefactor's Draught

Untap all creatures. Until end of turn, whenever a creature an opponent controls blocks, draw a card.
Draw a card.

Path of Discovery

Whenever a creature enters the battlefield under your control, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on the creature, then put the card back or put it into your graveyard.)

Kiora's Follower

Empress Galina

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

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.)

Spell Pierce

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

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.)