Merfolk Sovereign

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

Coralhelm Guide

{4}{U}: Target creature can't be blocked this turn.

Soothsayer Adept

{1}{U}, {T}: Draw a card, then discard a card.

Maritime Guard

Seafloor Oracle

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

Triton Shorethief

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.

Silvergill Douser

{T}: Target creature gets -X/-0 until end of turn, where X is the number of Merfolk and/or Faeries you control.

Test of Talents

Counter target instant or sorcery spell. Search its controller's graveyard, hand, and library for any number of cards with the same name as that spell and exile them. That player shuffles, then draws a card for each card exiled from their hand this way.

Kasmina's Transmutation

Enchant creature
Enchanted creature loses all abilities and has base power and toughness 1/1.

Paperfin Rascal

When Paperfin Rascal enters, clash with an opponent. If you win, put a +1/+1 counter on Paperfin Rascal. (Each clashing player reveals the top card of their library, then puts that card on the top or bottom. A player wins if their card had a higher mana value.)

Negate

Dreadwaters

Target player mills X cards, where X is the number of lands you control.

Revolutionary Rebuff

Counter target nonartifact spell unless its controller pays {2}.

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.

Prismwake Merrow

Flash
When Prismwake Merrow enters, target permanent becomes the color or colors of your choice until end of turn.

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Chilling Grasp

Tap up to two target creatures. Those creatures don't untap during their controller's next untap step.
Madness {3}{U} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Merrow Levitator

{T}: Target creature gains flying until end of turn.
Whenever you cast a blue spell, you may untap Merrow Levitator.

Scour All Possibilities

Scry 2, then draw a card.
Flashback {4}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

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.

Vodalian Arcanist

{T}: Add {C}. Spend this mana only to cast an instant or sorcery spell.

Mist-Cloaked Herald

Dazzling Lights

Target creature gets -3/-0 until end of turn.
Surveil 2. (Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

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.

No Escape

Counter target creature or planeswalker spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.
Scry 1.

Triton Shorestalker

Reject

Counter target creature or planeswalker spell unless its controller pays {3}. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Cancel

Mental Journey

Draw three cards.
Basic landcycling {1}{U} ({1}{U}, Discard this card: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.)

Rush of Ice

Tap target creature. It doesn't untap during its controller's next untap step.
Awaken 3—{4}{U} (If you cast this spell for {4}{U}, also put three +1/+1 counters on target land you control and it becomes a 0/0 Elemental creature with haste. It's still a land.)

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.

Traveler's Amulet

{1}, Sacrifice Traveler's Amulet: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.

Convolute

Counter target spell unless its controller pays {4}.

Spell Snuff

Counter target spell.
Fateful hour — If you have 5 or less life, draw a card.

Fallowsage

Whenever Fallowsage becomes tapped, you may draw a card.

Wilderness Hypnotist

{T}: Target red or green creature gets -2/-0 until end of turn.

Memory Drain

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.)

Thought Collapse

Counter target spell. Its controller mills three cards.

Crashing Tide

This spell has flash as long as you control a Merfolk.
Return target creature to its owner's hand.
Draw a card.

River Darter

River Darter can't be blocked by Dinosaurs.

Merrow Witsniper

When Merrow Witsniper enters, target player mills a card.

Island

Razorfin Abolisher

{1}{U}, {T}: Return target creature with a counter on it to its owner's hand.

Towering-Wave Mystic

Whenever Towering-Wave Mystic deals damage, target player mills that many cards.

Didn't Say Please

Roilmage's Trick

Converge — Creatures your opponents control get -X/-0 until end of turn, where X is the number of colors of mana spent to cast this spell.
Draw a card.

Salvager of Secrets

When Salvager of Secrets enters, return target instant or sorcery card from your graveyard to your hand.

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.

Coral Merfolk

Resculpt

Exile target artifact or creature. Its controller creates a 4/4 blue and red Elemental creature token.

Tempest Caller

When Tempest Caller enters, tap all creatures target opponent controls.

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.

Riverwise Augur

When Riverwise Augur enters, draw three cards, then put two cards from your hand on top of your library in any order.

Claustrophobia

Enchant creature
When Claustrophobia enters, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

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.

Headwater Sentries

Hornswoggle

Counter target creature spell. You create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Ink Dissolver

Kinship — At the beginning of your upkeep, you may look at the top card of your library. If it shares a creature type with Ink Dissolver, you may reveal it. If you do, each opponent mills three cards.

Deeptread Merrow

{U}: Deeptread Merrow gains islandwalk until end of turn. (It can't be blocked as long as defending player controls an Island.)

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}.)

Unexplained Disappearance

Return target creature to its owner's hand.
Surveil 1. (Look at the top card of your library. You may put that card into your graveyard.)

Storm Sculptor

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

Glimpse of Freedom

Draw a card.
Escape—{2}{U}, Exile five other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Raving Visionary

{U}, {T}: Draw a card, then discard a card.
Delirium — {2}{U}, {T}: Draw a card. Activate only if there are four or more card types among cards in your graveyard.

Kefnet's Monument

Blue creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, target creature an opponent controls doesn't untap during its controller's next untap step.