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.

Ripples of Potential

Proliferate, then choose any number of permanents you control that had a counter put on them this way. Those permanents phase out. (To proliferate, choose any number of permanents and/or players, then give each another counter of each kind already there. Treat phased-out permanents and anything attached to them as though they don't exist until their controller's next turn.)

Heroic Intervention

Permanents you control gain hexproof and indestructible until end of turn.

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.

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.)

Command Tower

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

Fallowsage

Whenever Fallowsage becomes tapped, you may draw a card.

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.

Streambed Aquitects

{T}: Target Merfolk creature gets +1/+1 and gains islandwalk until end of turn. (It can't be blocked as long as defending player controls an Island.)
{T}: Target land becomes an Island until end of turn.

Hakbal of the Surging Soul

At the beginning of combat on your turn, each Merfolk creature you control 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 exploring creature, then put the card back or put it into your graveyard.)
Whenever Hakbal of the Surging Soul attacks, you may put a land card from your hand onto the battlefield. If you don't, draw a card.

Elven Chorus

You may look at the top card of your library any time.
You may cast creature spells from the top of your library.
Creatures you control have "{T}: Add one mana of any color."

Harvest Season

Search your library for up to X basic land cards, where X is the number of tapped creatures you control, put those cards onto the battlefield tapped, then shuffle.

Novijen, Heart of Progress

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

Throne of the God-Pharaoh

At the beginning of your end step, each opponent loses life equal to the number of tapped creatures you control.

Vineglimmer Snarl

As Vineglimmer Snarl enters the battlefield, you may reveal a Forest or Island card from your hand. If you don't, Vineglimmer Snarl enters the battlefield tapped.
{T}: Add {G} or {U}.

Merrow Commerce

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

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.

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Alchemist's Refuge

{T}: Add {C}.
{G}{U}, {T}: You may cast spells this turn as though they had flash.

Wanderwine Prophets

Champion a Merfolk (When this enters the battlefield, 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.

Tishana's Tidebinder

Flash
When Tishana's Tidebinder enters the battlefield, counter up to one target activated or triggered ability. If an ability of an artifact, creature, or planeswalker is countered this way, that permanent loses all abilities for as long as Tishana's Tidebinder remains on the battlefield. (Mana abilities can't be targeted.)

Seedborn Muse

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

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.

Temple of Mystery

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

Secluded Courtyard

As Secluded Courtyard 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 or activate an ability of a creature source of the chosen type.

Unnatural Restoration

Return target permanent card from your graveyard to your hand. Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Rampant Growth

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

Realmwalker

Changeling (This card is every creature type.)
As Realmwalker enters the battlefield, choose a creature type.
You may look at the top card of your library any time.
You may cast creature spells of the chosen type from the top of your library.

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.

Seafloor Oracle

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

Mist-Cloaked Herald

Rejuvenating Springs

Rejuvenating Springs enters the battlefield tapped unless you have two or more opponents.
{T}: Add {G} or {U}.

Counterspell

Intruder Alarm

Creatures don't untap during their controllers' untap steps.
Whenever a creature enters the battlefield, untap all creatures.

Rapid Hybridization

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

Cosi's Trickster

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

Otawara, Soaring City

{T}: Add {U}.
Channel — {3}{U}, Discard Otawara, Soaring City: Return target artifact, creature, enchantment, or planeswalker to its owner's hand. This ability costs {1} less to activate for each legendary creature you control.

Merfolk Sovereign

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

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.

Krosan Grip

Split second (As long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abilities.)
Destroy target artifact or enchantment.

Rhystic Study

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

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.

Deeproot Elite

Whenever another Merfolk enters the battlefield under your control, put a +1/+1 counter on target Merfolk you control.

Sol Ring

Merfolk Mistbinder

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}.)

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.

Dreamroot Cascade

Dreamroot Cascade enters the battlefield tapped unless you control two or more other lands.
{T}: Add {G} or {U}.

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 the battlefield, 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.

Arcane Signet

Kiora's Follower

True-Name Nemesis

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

Island

Reflections of Littjara

As Reflections of Littjara enters the battlefield, 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.)

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.

Botanical Sanctum

Botanical Sanctum enters the battlefield tapped unless you control two or fewer other lands.
{T}: Add {G} or {U}.

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.)

Forest

Reliquary Tower

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

Triumph of the Hordes

Until end of turn, creatures you control get +1/+1 and gain trample and infect. (Creatures with infect deal damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Herald of Secret Streams

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

Vodalian Hexcatcher

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

Breeding Pool

({T}: Add {G} or {U}.)
As Breeding Pool enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

Raise the Palisade

Choose a creature type. Return all creatures that aren't of the chosen type to their owners' hands.

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.

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.)

Negate

Yavimaya Coast

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

Inspiring Call

Draw a card for each creature you control with a +1/+1 counter on it. Those creatures gain indestructible until end of turn. (Damage and effects that say "destroy" don't destroy them.)

Quest for Renewal

Whenever a creature you control becomes tapped, you may put a quest counter on Quest for Renewal.
As long as there are four or more quest counters on Quest for Renewal, untap all creatures you control during each other player's untap step.

Seahunter

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

Talisman of Curiosity

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

Tidechannel Pathway

Barkchannel Pathway

Barkchannel Pathway // Tidechannel Pathway

Robe of the Archmagi

Whenever equipped creature deals combat damage to a player, you draw that many cards.
Equip {4}
Equip Shaman, Warlock, or Wizard {1}

Pongify

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

Hardened Scales

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

Guardian Project

Whenever a nontoken creature enters the battlefield under your control, if it doesn't have the same name as another creature you control or a creature card in your graveyard, draw a card.

Cultivate

Distant Melody

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

Cavern of Souls

As Cavern of Souls 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, and that spell can't be countered.

Growth Spiral

Draw a card. You may put a land card from your hand onto the battlefield.

Karn's Bastion

{T}: Add {C}.
{4}, {T}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

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.)

Hinterland Harbor

Hinterland Harbor enters the battlefield tapped unless you control a Forest or an Island.
{T}: Add {G} or {U}.

Doubling Season

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.
If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead.

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.

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.

Deeproot Pilgrimage

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

Tezzeret's Gambit

({U/P} can be paid with either {U} or 2 life.)
Draw two cards, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

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.

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.

Boseiju, Who Endures

{T}: Add {G}.
Channel — {1}{G}, Discard Boseiju, Who Endures: Destroy target artifact, enchantment, or nonbasic land an opponent controls. That player may search their library for a land card with a basic land type, put it onto the battlefield, then shuffle. This ability costs {1} less to activate for each legendary creature you control.

Beast Within

Destroy target permanent. Its controller creates a 3/3 green Beast creature token.

Lord of Atlantis

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

Merrow Reejerey

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

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.)

Herald's Horn

As Herald's Horn enters the battlefield, choose a creature type.
Creature spells you cast of the chosen type cost {1} less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

Deeproot Historian

Merfolk and Druid cards in your graveyard have retrace. (You may cast cards with retrace from your graveyard by discarding a land card in addition to paying their other costs.)