Memorial to Genius

This land enters tapped.
{T}: Add {U}.
{4}{U}, {T}, Sacrifice this land: Draw two cards.

Slinn Voda, the Rising Deep

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

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.

Reliquary Tower

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

Misdirection

You may exile a blue card from your hand rather than pay this spell's mana cost.
Change the target of target spell with a single target.

Jiang Yanggu, Wildcrafter

Each creature you control with a +1/+1 counter on it has "{T}: Add one mana of any color."
−1: Put a +1/+1 counter on target creature.

Merrow Reejerey

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

Omen of the Sea

Flash (You may cast this spell any time you could cast an instant.)
When this enchantment enters, scry 2, then draw a card.
{2}{U}, Sacrifice this enchantment: 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.)

Curious Obsession

Enchant creature
Enchanted creature gets +1/+1 and has "Whenever this creature deals combat damage to a player, you may draw a card."
At the beginning of your end step, if you didn't attack with a creature this turn, sacrifice this Aura.

Deeproot Champion

Whenever you cast a noncreature spell, put a +1/+1 counter on this creature.

Unwind

Counter target noncreature spell. Untap up to three lands.

Chart a Course

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

Mist-Cloaked Herald

Sleep

Tap all creatures target player controls. Those creatures don't untap during that player's next untap step.

Aquatic Incursion

When this enchantment 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.

Scroll Thief

Whenever this creature deals combat damage to a player, draw a card.

Wilderness Reclamation

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

Memorial to Unity

This land enters tapped.
{T}: Add {G}.
{2}{G}, {T}, Sacrifice this land: Look at the top five cards of your library. You may reveal a creature card from among them and put it into your hand. Then put the rest on the bottom of your library in a random order.

Tidal Warrior

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

Command Tower

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

Incongruity

Exile target creature. That creature's controller creates a 3/3 green Frog Lizard creature token.

Incubation

Look at the top five cards of your library. You may reveal a creature card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Incubation // Incongruity

Jadelight Ranger

When this creature enters, it explores, then it explores again. (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 this creature, then put the card back or put it into your graveyard. Then repeat this process.)

Deeproot Elite

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

Zegana, Utopian Speaker

When Zegana enters, 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.

Vanquisher's Banner

As this artifact enters, 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.

Desert of the Indomitable

This land enters tapped.
{T}: Add {G}.
Cycling {1}{G} ({1}{G}, Discard this card: Draw a card.)

Forerunner of the Heralds

When this creature enters, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.
Whenever another Merfolk you control enters, put a +1/+1 counter on this creature.

Hinterland Harbor

This land enters tapped unless you control a Forest or an Island.
{T}: Add {G} or {U}.

Jade Guardian

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
When this creature enters, put a +1/+1 counter on target Merfolk you control.

Cold-Eyed Selkie

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

Gateway Plaza

This land enters tapped.
When this land enters, sacrifice it unless you pay {1}.
{T}: Add one mana of any color.

True-Name Nemesis

As this creature enters, choose a player.
This creature has protection from the chosen player.

Breeding Pool

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

Kiora's Follower

Island

Field of Ruin

{T}: Add {C}.
{2}, {T}, Sacrifice this land: Destroy target nonbasic land an opponent controls. Each player searches their library for a basic land card, puts it onto the battlefield, then shuffles.

Kumena's Awakening

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
At the beginning of your upkeep, each player draws a card. If you have the city's blessing, instead only you draw a card.

Merfolk Skydiver

Flying
When this creature enters, 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.)

Archetype of Imagination

Creatures you control have flying.
Creatures your opponents control lose flying and can't have or gain flying.

Swift Warden

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

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.

Counterspell

Lonely Sandbar

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

Jungleborn Pioneer

When this creature enters, create a 1/1 blue Merfolk creature token with hexproof. (It can't be the target of spells or abilities your opponents control.)

Forest

Lord of Atlantis

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

Merfolk Sovereign

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

Tempest Caller

When this creature enters, tap all creatures target opponent controls.

Guardian Project

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

Kumena, Tyrant of Orazca

Tap another untapped Merfolk you control: Kumena 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.

Growth Spiral

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

Herald of Secret Streams

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

Seafloor Oracle

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

Tishana, Voice of Thunder

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

Storm Sculptor

This creature can't be blocked.
When this creature enters, return a creature you control to its owner's hand.

Desert of the Mindful

This land enters tapped.
{T}: Add {U}.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)

Shapers' Sanctuary

Whenever a creature you control becomes the target of a spell or ability an opponent controls, you may draw a card.

Aqueous Form

Enchant creature
Enchanted creature can't be blocked.
Whenever enchanted creature attacks, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Woodland Stream

This land enters tapped.
{T}: Add {G} or {U}.

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.)

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.)

Terminal Moraine

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

Broken Bond

Destroy target artifact or enchantment. You may put a land card from your hand onto the battlefield.

Essence Scatter

The Immortal Sun

Players can't activate planeswalkers' loyalty abilities.
At the beginning of your draw step, draw an additional card.
Spells you cast cost {1} less to cast.
Creatures you control get +1/+1.

Syncopate

Counter target spell unless its controller pays {X}. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Ordeal of Thassa

Enchant creature
Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice this Aura.
When you sacrifice this Aura, draw two cards.

Simic Guildgate

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.

Tatyova, Benthic Druid

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

Tranquil Thicket

This land enters tapped.
{T}: Add {G}.
Cycling {G} ({G}, Discard this card: Draw a card.)

River Sneak

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

Jade Bearer

When this creature enters, put a +1/+1 counter on another target Merfolk you control.

Wistful Selkie

Thassa, Deep-Dwelling

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature.
At the beginning of your end step, exile up to one other target creature you control, then return that card to the battlefield under your control.
{3}{U}: Tap another target creature.

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.

Harbinger of the Tides

You may cast this card 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 this creature enters, you may return target tapped creature an opponent controls to its owner's hand.

Arrester's Admonition

Return target creature to its owner's hand.
Addendum — If you cast this spell during your main phase, draw a card.

Inkfathom Divers

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
When this creature enters, look at the top four cards of your library, then put them back in any order.

Aether Tunnel

Enchant creature
Enchanted creature gets +1/+0 and can't be blocked.

Essence Capture

Counter target creature spell. Put a +1/+1 counter on up to one target creature you control.

Combine Guildmage

{1}{G}, {T}: This turn, each creature you control enters with an additional +1/+1 counter on it.
{1}{U}, {T}: Move a +1/+1 counter from target creature you control onto another target creature you control.

Open the Gates

Search your library for a basic land card or Gate card, reveal it, put it into your hand, then shuffle.

Fated Infatuation

Create a token that's a copy of target creature you control. If it's your turn, scry 2.

Merfolk Mistbinder

Renata, Called to the Hunt

Renata's power is equal to your devotion to green. (Each {G} in the mana costs of permanents you control counts toward your devotion to green.)
Each other creature you control enters with an additional +1/+1 counter on it.