Lonely Sandbar

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

Secrets of the Key

Investigate. If this spell was cast from a graveyard, investigate twice instead. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")
Flashback {3}{U}

Towering-Wave Mystic

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

Mystic Subdual

Flash
Enchant creature
Enchanted creature gets -2/-0 and loses all abilities. (Mutating onto the creature won't give it new abilities. It can gain abilities in other ways.)

Claustrophobia

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

Tidebinder Mage

When Tidebinder Mage enters, tap target red or green creature an opponent controls. That creature doesn't untap during its controller's untap step for as long as you control Tidebinder Mage.

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.

Voda Sea Scavenger

Domain — When Voda Sea Scavenger enters, look at the top X cards of your library, where X is the number of basic land types among lands you control. You may put one of those cards on top of your library. Put the rest on the bottom of your library in a random order.

Starlit Mantle

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature you control
When Starlit Mantle enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

Coralhelm Guide

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

High Tide

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.

Triton Waverider

Constellation — Whenever an enchantment you control enters, Triton Waverider gains flying until end of turn.

Merfolk Looter

Fear of Death

Enchant creature
When Fear of Death enters, mill two cards. (Put the top two cards of your library into your graveyard.)
Enchanted creature gets -X/-0, where X is the number of cards in your graveyard.

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.)

Rootwater Hunter

{T}: Rootwater Hunter deals 1 damage to any target.

Triton Tactics

Up to two target creatures each get +0/+3 until end of turn. Untap those creatures. At this turn's next end of combat, tap each creature that was blocked by one of those creatures this turn and it doesn't untap during its controller's next untap step.

Empress Galina

{U}{U}, {T}: Gain control of target legendary permanent. (This effect lasts indefinitely.)

Guard Gomazoa

Defender, flying
Prevent all combat damage that would be dealt to Guard Gomazoa.

Planar Incision

Exile target artifact or creature, then return it to the battlefield under its owner's control with a +1/+1 counter on it.

Wake Thrasher

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

Tidal Wave

Create a 5/5 blue Wall creature token with defender. Sacrifice it at the beginning of the next end step.

Coma Veil

Enchant artifact or creature
Enchanted permanent doesn't untap during its controller's untap step.

Syphon Essence

Counter target creature or planeswalker spell. Create a Blood token. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this artifact: Draw a card.")

Scroll Thief

Whenever Scroll Thief deals combat damage to a player, draw a card.

Tortoise Formation

Creatures you control gain shroud until end of turn. (They can't be the targets of spells or abilities.)

Mystic Remora

Cumulative upkeep {1} (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.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Dreadwaters

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

Merfolk Sovereign

Other Merfolk creatures you control get +1/+1.
{T}: Target Merfolk creature 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.

Disruption Protocol

As an additional cost to cast this spell, tap an untapped artifact you control or pay {1}.
Counter target spell.

Tidal Courier

When Tidal Courier enters, reveal the top four cards of your library. Put all Merfolk cards revealed this way into your hand and the rest on the bottom of your library in any order.
{3}{U}: Tidal Courier gains flying until end of turn.

Startling Development

Until end of turn, target creature becomes a blue Serpent with base power and toughness 4/4.
Cycling {1} ({1}, Discard this card: Draw a card.)

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.

Fading Hope

Return target creature to its owner's hand. If its mana value was 3 or less, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

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.

Cumber Stone

Creatures your opponents control get -1/-0.

Mist-Cloaked Herald

Unquenchable Thirst

Enchant creature
When Unquenchable Thirst enters, if you control a Desert or there is a Desert card in your graveyard, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

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.

Gray Harbor Merfolk

Gray Harbor Merfolk can't be blocked.
Gray Harbor Merfolk gets +2/+0 as long as you control a commander that's a creature or planeswalker.

Locked in the Cemetery

Enchant creature
When Locked in the Cemetery enters, if there are five or more cards in your graveyard, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

Master of Waves

Protection from red
Elemental creatures you control get +1/+1.
When Master of Waves enters, create a number of 1/0 blue Elemental creature tokens equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Eluge, the Shoreless Sea

Eluge's power and toughness are each equal to the number of Islands you control.
Whenever Eluge enters or attacks, put a flood counter on target land. It's an Island in addition to its other types for as long as it has a flood counter on it.
The first instant or sorcery spell you cast each turn costs {U} (or {1}) less to cast for each land you control with a flood counter on it.

Cradle of Safety

Flash
Enchant creature you control
When Cradle of Safety enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

Soothsayer Adept

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

Blighted Cataract

{T}: Add {C}.
{5}{U}, {T}, Sacrifice Blighted Cataract: Draw two cards.

Umara Entangler

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Corrupted Conscience

Enchant creature
You control enchanted creature.
Enchanted creature has infect. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Disdainful Stroke

Counter target spell with mana value 4 or greater.

Merrow Reejerey

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

Maritime Guard

Sensory Deprivation

Enchant creature
Enchanted creature gets -3/-0.

Merfolk Wayfinder

Flying
When Merfolk Wayfinder enters, reveal the top three cards of your library. Put all Island cards revealed this way into your hand and the rest on the bottom of your library in any order.

Merfolk Mesmerist

Erratic Mutation

Choose target creature. Reveal cards from the top of your library until you reveal a nonland card. That creature gets +X/-X until end of turn, where X is that card's mana value. Put all cards revealed this way on the bottom of your library in any order.

Volshe Tideturner

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

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Island

Concentrate

Vow of Flight

Enchant creature
Enchanted creature gets +2/+2, has flying, and can't attack you or planeswalkers you control.

Nyxborn Triton

Bestow {4}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
Enchanted creature gets +2/+3.

Engulf the Shore

Return to their owners' hands all creatures with toughness less than or equal to the number of Islands you control.

Coral Merfolk

Grasp of Phantoms

Put target creature on top of its owner's library.
Flashback {7}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Essence Scatter

Sleep of the Dead

Tap target creature. It doesn't untap during its controller's next untap step.
Escape—{2}{U}, Exile three other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Witness Protection

Enchant creature
Enchanted creature loses all abilities and is a green and white Citizen creature with base power and toughness 1/1 named Legitimate Businessperson. (It loses all other colors, card types, creature types, and names.)

Candlekeep Sage

Commander creatures you own have "When this creature enters or leaves the battlefield, draw a card."

Crashing Tide

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

Armguard Familiar

Ward {2} (Whenever this permanent becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
Equipped creature gets +2/+1 and has ward {2}.
Reconfigure {4} ({4}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn't a creature.)

Tidal Warrior

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

Emperor Mihail II

You may look at the top card of your library any time.
You may cast Merfolk spells from the top of your library.
Whenever you cast a Merfolk spell, you may pay {1}. If you do, create a 1/1 blue Merfolk creature token.