Naturalize

Island

Temple of Mystery

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

Deeproot Elite

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

Merfolk Skydiver

Flying
When Merfolk Skydiver 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.)

Negate

Swift Warden

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

Beastmaster Ascension

Whenever a creature you control attacks, you may put a quest counter on Beastmaster Ascension.
As long as Beastmaster Ascension has seven or more quest counters on it, creatures you control get +5/+5.

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

Growth Spiral

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

Merfolk Branchwalker

When Merfolk Branchwalker enters, 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 this creature, then put the card back or put it into your graveyard.)

Merrow Commerce

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

Counterspell

Silvergill Adept

As an additional cost to cast this spell, reveal a Merfolk card from your hand or pay {3}.
When Silvergill Adept enters, draw a card.

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.

Thornwood Falls

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

Fabled Passage

{T}, Sacrifice Fabled Passage: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Then if you control four or more lands, untap that land.

Jungleborn Pioneer

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

Triton Shorestalker

Simic Charm

Choose one —
• Target creature gets +3/+3 until end of turn.
• Permanents you control gain hexproof until end of turn.
• Return target creature to its owner's hand.

Jadelight Ranger

When Jadelight Ranger 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.)

Breeding Pool

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

Gaea's Skyfolk

Castle Vantress

Castle Vantress enters tapped unless you control an Island.
{T}: Add {U}.
{2}{U}{U}, {T}: Scry 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.)

Merfolk Trickster

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

Vineshaper Mystic

When Vineshaper Mystic enters, put a +1/+1 counter on each of up to two target Merfolk you control.

True-Name Nemesis

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

Lord of Atlantis

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

Cursecatcher

Sacrifice Cursecatcher: Counter target instant or sorcery spell unless its controller pays {1}.

Simic Growth Chamber

Simic Growth Chamber enters tapped.
When Simic Growth Chamber enters, return a land you control to its owner's hand.
{T}: Add {G}{U}.

Hinterland Harbor

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

Castle Garenbrig

Castle Garenbrig enters tapped unless you control a Forest.
{T}: Add {G}.
{2}{G}{G}, {T}: Add six {G}. Spend this mana only to cast creature spells or activate abilities of creatures.

Mist-Cloaked Herald

Wake Thrasher

Whenever a permanent you control becomes untapped, Wake Thrasher gets +1/+1 until end of turn.

Merfolk Mistbinder

Heroic Intervention

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

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.

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.

Forest

Woodland Stream

Woodland Stream enters tapped.
{T}: Add {G} or {U}.

River Sneak

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

Lumbering Falls

Lumbering Falls enters tapped.
{T}: Add {G} or {U}.
{2}{G}{U}: Lumbering Falls becomes a 3/3 green and blue Elemental creature with hexproof until end of turn. It's still a land.

Kumena's Speaker

Kumena's Speaker gets +1/+1 as long as you control another Merfolk or an Island.

Merfolk Sovereign

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

Merrow Reejerey

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