Preordain

Scry 2, then draw a card. (To 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.)

Mystic Snake

Flash
When Mystic Snake enters the battlefield, counter target spell.

Natural State

Destroy target artifact or enchantment with mana value 3 or less.

Scent of Brine

Reveal any number of blue cards in your hand. Counter target spell unless its controller pays {1} for each card revealed this way.

Nephalia Smuggler

{3}{U}, {T}: Exile another target creature you control, then return that card to the battlefield under your control.

Mist Dancer

Flying
Other Merfolk you control get +1/+0 and have flying.
Encore {5}{U}{U} ({5}{U}{U}, Exile this card from your graveyard: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)

Reality

Illusion

Target spell or permanent becomes the color of your choice until end of turn.

Illusion // Reality

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}.)

Utopia Sprawl

Enchant Forest
As Utopia Sprawl enters the battlefield, choose a color.
Whenever enchanted Forest is tapped for mana, its controller adds an additional one mana of the chosen color.

Sol Ring

Proft's Eidetic Memory

When Proft's Eidetic Memory enters the battlefield, draw a card.
You have no maximum hand size.
At the beginning of combat on your turn, if you've drawn more than one card this turn, put X +1/+1 counters on target creature you control, where X is the number of cards you've drawn this turn minus one.

Lightning Greaves

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

Greater Good

Sacrifice a creature: Draw cards equal to the sacrificed creature's power, then discard three cards.

Blizzard Strix

Flash
Flying
When Blizzard Strix enters the battlefield, if you control another snow permanent, exile target permanent other than Blizzard Strix. Return that card to the battlefield under its owner's control at the beginning of the next end step.

Flooded Grove

{T}: Add {C}.
{G/U}, {T}: Add {G}{G}, {G}{U}, or {U}{U}.

Hinterland Harbor

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

Sentinel of the Pearl Trident

Flash
When Sentinel of the Pearl Trident enters the battlefield, you may exile target historic permanent you control. If you do, return that card to the battlefield under its owner's control at the beginning of the next end step. (Artifacts, legendaries, and Sagas are historic.)

Lonis, Cryptozoologist

Whenever another nontoken creature enters the battlefield under your control, investigate.
{T}, Sacrifice X Clues: Target opponent reveals the top X cards of their library. You may put a nonland permanent card with mana value X or less from among them onto the battlefield under your control. That player puts the rest on the bottom of their library in a random order.

Tidechannel Pathway

Barkchannel Pathway

Barkchannel Pathway // Tidechannel Pathway

Scent of Ivy

Reveal any number of green cards in your hand. Target creature gets +X/+X until end of turn, where X is the number of cards revealed this way.

Trygon Predator

Flying
Whenever Trygon Predator deals combat damage to a player, you may destroy target artifact or enchantment that player controls.

Jolrael, Mwonvuli Recluse

Whenever you draw your second card each turn, create a 2/2 green Cat creature token.
{4}{G}{G}: Until end of turn, creatures you control have base power and toughness X/X, where X is the number of cards in your hand.

Elvish Rejuvenator

When Elvish Rejuvenator enters the battlefield, look at the top five cards of your library. You may put a land card from among them onto the battlefield tapped. Put the rest on the bottom of your library in a random order.

Fblthp, the Lost

When Fblthp, the Lost enters the battlefield, draw a card. If it entered from your library or was cast from your library, draw two cards instead.
When Fblthp becomes the target of a spell, shuffle Fblthp into its owner's library.

Negate

Jolrael, Voice of Zhalfir

At the beginning of combat on your turn, up to one target land you control becomes an X/X green and blue Bird creature with flying and haste until end of turn, where X is the number of cards in your hand. It's still a land.
Whenever a land creature you control deals combat damage to a player, draw a card.

Quandrix Command

Choose two —
• Return target creature or planeswalker to its owner's hand.
• Counter target artifact or enchantment spell.
• Put two +1/+1 counters on target creature.
• Target player shuffles up to three target cards from their graveyard into their library.

Duggan, Private Detective

Duggan's power and toughness are each equal to the number of cards in your hand.
Whenever Duggan enters the battlefield or attacks, investigate.
The Most Important Punch in History — {1}{G}, {T}: Duggan deals damage equal to twice its power to another target creature. Activate only once.

Boreal Druid

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

Rejuvenating Springs

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

Wood Elves

When Wood Elves enters the battlefield, search your library for a Forest card, put that card onto the battlefield, then shuffle.

Overflowing Basin

Ivy Seer

{2}{G}, {T}: Reveal any number of green cards in your hand. Target creature gets +X/+X until end of turn, where X is the number of cards revealed this way.

Arbor Elf

Farhaven Elf

When Farhaven Elf enters the battlefield, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Singer of Swift Rivers

Flash
When Singer of Swift Rivers enters the battlefield, put a shield counter on another target creature you control. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
You may cast Merfolk spells as though they had flash.

Fyndhorn Elves

Elvish Mystic

Tail the Suspect

Investigate. You may play an additional land this turn. (Then exile this card. You may cast the creature later from exile.)

Kellan, Inquisitive Prodigy

Flying, vigilance
Whenever Kellan, Inquisitive Prodigy attacks, destroy up to one target artifact. If you controlled that permanent, draw a card.

Kellan, Inquisitive Prodigy // Tail the Suspect

Venser, Shaper Savant

Flash
When Venser, Shaper Savant enters the battlefield, return target spell or permanent to its owner's hand.

Bala Ged Sanctuary

Bala Ged Sanctuary enters the battlefield tapped.
{T}: Add {G}.

Bala Ged Recovery

Return target card from your graveyard to your hand.

Bala Ged Recovery // Bala Ged Sanctuary

Scavenger Grounds

{T}: Add {C}.
{2}, {T}, Sacrifice a Desert: Exile all graveyards.

Llanowar Elves

Frilled Mystic

Flash
When Frilled Mystic enters the battlefield, you may counter target spell.

Life's Legacy

As an additional cost to cast this spell, sacrifice a creature.
Draw cards equal to the sacrificed creature's power.

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.")

Overgrowth

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G}{G}.

Rime Tender

{T}: Untap another target snow permanent.

Inner Calm, Outer Strength

Target creature gets +X/+X until end of turn, where X is the number of cards in your hand.

Springbloom Druid

When Springbloom Druid enters the battlefield, you may sacrifice a land. If you do, search your library for up to two basic land cards, put them onto the battlefield tapped, then shuffle.

Command Tower

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

Ohran Frostfang

Attacking creatures you control have deathtouch.
Whenever a creature you control deals combat damage to a player, draw a card.

Snow-Covered Island

Risen Reef

Whenever Risen Reef or another Elemental enters the battlefield under your control, look at the top card of your library. If it's a land card, you may put it onto the battlefield tapped. If you don't put the card onto the battlefield, put it into your hand.

Brine Seer

{2}{U}, {T}: Reveal any number of blue cards in your hand. Counter target spell unless its controller pays {1} for each card revealed this way.

Marit Lage's Slumber

Whenever Marit Lage's Slumber or another snow permanent enters the battlefield under your control, scry 1.
At the beginning of your upkeep, if you control ten or more snow permanents, sacrifice Marit Lage's Slumber. If you do, create Marit Lage, a legendary 20/20 black Avatar creature token with flying and indestructible.

Oppressive Will

Counter target spell unless its controller pays {1} for each card in your hand.

Wild Growth

Enchant land
Whenever enchanted land is tapped for mana, its controller adds an additional {G}.

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.

Merfolk Sovereign

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

Botanical Sanctum

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

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control.)
Equip {1}

Snow-Covered Forest

Waterlogged Grove

{T}, Pay 1 life: Add {G} or {U}.
{1}, {T}, Sacrifice Waterlogged Grove: Draw a card.

Identity Thief

Whenever Identity Thief attacks, you may exile another target nontoken creature. If you do, Identity Thief becomes a copy of that creature until end of turn. Return the exiled card to the battlefield under its owner's control at the beginning of the next end step.

Yavimaya Coast

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

Exotic Orchard

{T}: Add one mana of any color that a land an opponent controls could produce.

Maro

Maro's power and toughness are each equal to the number of cards in your hand.

Ice-Fang Coatl

Flash
Flying
When Ice-Fang Coatl enters the battlefield, draw a card.
Ice-Fang Coatl has deathtouch as long as you control at least three other snow permanents.

Aether Mutation

Return target creature to its owner's hand. Create X 1/1 green Saproling creature tokens, where X is that creature's mana value.

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.

Meneldor, Swift Savior

Flying
Whenever Meneldor, Swift Savior deals combat damage to a player, exile up to one target creature you own, then return it to the battlefield under your control.

Sculptor of Winter

Mulldrifter

Flying
When Mulldrifter enters the battlefield, draw two cards.
Evoke {2}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters the battlefield.)

Dreamroot Cascade

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

Glittering Frost

Enchant land
Enchanted land is snow.
Whenever enchanted land is tapped for mana, its controller adds an additional one mana of any color.

Coiling Oracle

When Coiling Oracle enters the battlefield, reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put that card into your hand.

Nature's Claim

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

Coldsteel Heart

Coldsteel Heart enters the battlefield tapped.
As Coldsteel Heart enters the battlefield, choose a color.
{T}: Add one mana of the chosen color.

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.)