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.

Guardian of Tazeem

Flying
Landfall — Whenever a land you control enters, tap target creature an opponent controls. If that land is an Island, that creature doesn't untap during its controller's next untap step.

Lingering Mirage

Enchant land
Enchanted land is an Island.
Cycling {2} ({2}, Discard this card: Draw a card.)

Quicksilver Fountain

At the beginning of each player's upkeep, that player puts a flood counter on target non-Island land they control of their choice. That land is an Island for as long as it has a flood counter on it.
At the beginning of each end step, if all lands on the battlefield are Islands, remove all flood counters from them.

Sealock Monster

Sealock Monster can't attack unless defending player controls an Island.
{5}{U}{U}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
When Sealock Monster becomes monstrous, target land becomes an Island in addition to its other types.

Sea's Claim

Enchant land (Target a land as you cast this. This card enters attached to that land.)
Enchanted land is an Island.

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.

The Flood of Mars

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Water Always Wins — Whenever The Flood of Mars attacks, put a flood counter on another target creature or land. If it's a creature, it becomes a copy of The Flood of Mars. If it's a land, it becomes an Island in addition to its other types.

Xolatoyac, the Smiling Flood

Whenever Xolatoyac, the Smiling Flood enters or attacks, 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.
At the beginning of your end step, untap each permanent you control with a counter on it.

Tidal Warrior

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

Tide Shaper

Kicker {1} (You may pay an additional {1} as you cast this spell.)
When Tide Shaper enters, 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.

Reef Shaman

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

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.

Spreading Seas

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

Mystic Compass

{1}, {T}: Target land becomes the basic land type of your choice until end of turn.

Dream Thrush

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

Tideshaper Mystic

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

Dryad of the Ilysian Grove

You may play an additional land on each of your turns.
Lands you control are every basic land type in addition to their other types.

Illusionary Terrain

Cumulative upkeep {2} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
As Illusionary Terrain enters, choose two basic land types.
Basic lands of the first chosen type are the second chosen type.

Harbinger of the Seas

Lord of Atlantis

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

Phantasmal Terrain

Enchant land
As Phantasmal Terrain enters, choose a basic land type.
Enchanted land is the chosen type.

Convincing Mirage

Enchant land
As Convincing Mirage enters, choose a basic land type.
Enchanted land is the chosen type.

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.

Chasm Skulker

Whenever you draw a card, put a +1/+1 counter on Chasm Skulker.
When Chasm Skulker dies, create X 1/1 blue Squid creature tokens with islandwalk, where X is the number of +1/+1 counters on Chasm Skulker. (They can't be blocked as long as defending player controls an Island.)

Colossal Whale

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever Colossal Whale attacks, you may exile target creature defending player controls until Colossal Whale leaves the battlefield. (That creature returns under its owner's control.)

Coral Barrier

Defender (This creature can't attack.)
When Coral Barrier enters, create a 1/1 blue Squid creature token with islandwalk. (It can't be blocked as long as defending player controls an Island.)

Mirror Entity

Changeling (This card is every creature type.)
{X}: Until end of turn, creatures you control have base power and toughness X/X and gain all creature types.

Fishliver Oil

Enchant creature (Target a creature as you cast this. This card enters attached to that creature.)
Enchanted creature has islandwalk. (It can't be blocked as long as defending player controls an Island.)

Grayscaled Gharial

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Inkfathom Divers

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

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.)

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.)

Meandering Towershell

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever Meandering Towershell attacks, exile it. Return it to the battlefield under your control tapped and attacking at the beginning of the declare attackers step on your next turn.

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.

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.

Rootwater Commando

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.

Octomancer

Gift an Octopus (You may promise an opponent a gift as you cast this spell. If you do, when it enters, they create an 8/8 blue Octopus creature token.)
At the beginning of each end step, create a token that's a copy of target creature token that entered the battlefield this turn.

Adrix and Nev, Twincasters

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
If one or more tokens would be created under your control, twice that many of those tokens are created instead.

Forgotten Ancient

Whenever a player casts a spell, you may put a +1/+1 counter on Forgotten Ancient.
At the beginning of your upkeep, you may move any number of +1/+1 counters from Forgotten Ancient onto other creatures.

Aggressive Biomancy

Create X tokens that are copies of target creature you control, except they have "When this creature enters, it fights up to one target creature you don't control."

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.")

Aquatic Incursion

When Aquatic Incursion 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.

Life Finds a Way

Whenever a nontoken creature you control with power 4 or greater enters, populate. (Create a token that's a copy of a creature token you control.)

Druid's Deliverance

Prevent all combat damage that would be dealt to you this turn. Populate. (Create a token that's a copy of a creature token you control.)

Awakening Zone

At the beginning of your upkeep, you may create a 0/1 colorless Eldrazi Spawn creature token. It has "Sacrifice this creature: Add {C}."

Clone Legion

For each creature target player controls, create a token that's a copy of that creature.

Back from the Brink

Exile a creature card from your graveyard and pay its mana cost: Create a token that's a copy of that card. Activate only as a sorcery.

Baloth Cage Trap

If an opponent had an artifact enter the battlefield under their control this turn, you may pay {1}{G} rather than pay this spell's mana cost.
Create a 4/4 green Beast creature token.

Bestial Menace

Create a 1/1 green Snake creature token, a 2/2 green Wolf creature token, and a 3/3 green Elephant creature token.

Body of Research

Create a 0/0 green and blue Fractal creature token. Put X +1/+1 counters on it, where X is the number of cards in your library.

Brindle Shoat

When Brindle Shoat dies, create a 3/3 green Boar creature token.

Cackling Counterpart

Create a token that's a copy of target creature you control.
Flashback {5}{U}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Combine Chrysalis

Creature tokens you control have flying.
{2}{G}{U}, {T}, Sacrifice a token: Create a 4/4 green Beast creature token. Activate only as a sorcery.

Audience with Trostani

Create a 0/1 green Plant creature token, then draw cards equal to the number of differently named creature tokens you control.

Cloakwood Swarmkeeper

Gathered Swarm — Whenever one or more tokens you control enter, put a +1/+1 counter on Cloakwood Swarmkeeper.

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.

Faerie Slumber Party

Return all creatures to their owners' hands. For each opponent who controlled a creature returned this way, you create two 1/1 blue Faerie creature tokens with flying and "This creature can block only creatures with flying."

For the Common Good

Create X tokens that are copies of target token you control. Then tokens you control gain indestructible until your next turn. You gain 1 life for each token you control.

Old Gnawbone

Flying
Whenever a creature you control deals combat damage to a player, create that many Treasure tokens.

Parallel Lives

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.

Woodland Champion

Whenever one or more tokens you control enter, put that many +1/+1 counters on Woodland Champion.

Alrund's Epiphany

Create two 1/1 blue Bird creature tokens with flying. Take an extra turn after this one. Exile Alrund's Epiphany.
Foretell {4}{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.)

Trailblazer's Boots

Equipped creature has nonbasic landwalk. (It can't be blocked as long as defending player controls a nonbasic land.)
Equip {2}