Decanter of Endless Water

You have no maximum hand size.
{T}: Add one mana of any color.

Disallow

Counter target spell, activated ability, or triggered ability. (Mana abilities can't be targeted.)

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.

Sea Scryer

Intruder Alarm

Creatures don't untap during their controllers' untap steps.
Whenever a creature enters, untap all creatures.

Deepchannel Mentor

Blue creatures you control can't be blocked.

Slinn Voda, the Rising Deep

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
When Slinn Voda, the Rising Deep enters, if it was kicked, return all creatures to their owners' hands except for Merfolk, Krakens, Leviathans, Octopuses, and Serpents.

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.)

Deeproot Pilgrimage

Whenever one or more nontoken Merfolk you control become tapped, create a 1/1 blue Merfolk creature token with hexproof.

Reflections of Littjara

As Reflections of Littjara enters, choose a creature type.
Whenever you cast a spell of the chosen type, copy that spell. (A copy of a permanent spell becomes a token.)

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.

Inundate

Return all nonblue creatures to their owners' hands.

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.

Cavern of Souls

As Cavern of Souls enters, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type, and that spell can't be countered.

Terrain Generator

{T}: Add {C}.
{2}, {T}: You may put a basic land card from your hand onto the battlefield tapped.

Talrand, Sky Summoner

Whenever you cast an instant or sorcery spell, create a 2/2 blue Drake creature token with flying.

Military Intelligence

Whenever you attack with two or more creatures, draw a card.

Library Larcenist

Whenever Library Larcenist attacks, draw a card.

Triton Shorestalker

Midnight Clock

{T}: Add {U}.
{2}{U}: Put an hour counter on Midnight Clock.
At the beginning of each upkeep, put an hour counter on Midnight Clock.
When the twelfth hour counter is put on Midnight Clock, shuffle your hand and graveyard into your library, then draw seven cards. Exile Midnight Clock.

Distant Melody

Choose a creature type. Draw a card for each permanent you control of that type.

Vodalian Hexcatcher

Flash
Other Merfolk you control get +1/+1.
Sacrifice a Merfolk: Counter target noncreature spell unless its controller pays {1}.

Merfolk Trickster

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

Island

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.)

Mana Drain

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

Harbinger of the Seas

Crashing Tide

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

Arcane Lighthouse

{T}: Add {C}.
{1}, {T}: Until end of turn, creatures your opponents control lose hexproof and shroud and can't have hexproof or shroud.

Scroll Thief

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

Unsummon

Return target creature to its owner's hand.

River Sneak

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

Coralhelm Commander

Level up {1} ({1}: Put a level counter on this. Level up only as a sorcery.)
LEVEL 2-3
3/3
Flying
LEVEL 4+
4/4
Flying
Other Merfolk creatures you control get +1/+1.

Riptide Laboratory

{T}: Add {C}.
{1}{U}, {T}: Return target Wizard you control to its owner's hand.

Sea's Claim

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

Spreading Seas

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

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.

Seahunter

{3}, {T}: Search your library for a Merfolk permanent card, put it onto the battlefield, then shuffle.

Wash Out

Return all permanents of the color of your choice to their owners' hands.

Sigil Tracer

{1}{U}, Tap two untapped Wizards you control: Copy target instant or sorcery spell. You may choose new targets for the copy.

True-Name Nemesis

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

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Silvergill Douser

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

Sleep

Tap all creatures target player controls. Those creatures don't untap during that player's next untap step.

Wanderwine Prophets

Champion a Merfolk (When this enters, sacrifice it unless you exile another Merfolk you control. When this leaves the battlefield, that card returns to the battlefield.)
Whenever Wanderwine Prophets deals combat damage to a player, you may sacrifice a Merfolk. If you do, take an extra turn after this one.

Merfolk Sovereign

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

Tempest Caller

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

Fallowsage

Whenever Fallowsage becomes tapped, you may draw a card.

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.

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.

Tideshaper Mystic

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

Teferi's Ageless Insight

If you would draw a card except the first one you draw in each of your draw steps, draw two cards instead.

Tidal Warrior

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

Blustersquall

Tap target creature you don't control.
Overload {3}{U} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Kindred Discovery

As Kindred Discovery enters, choose a creature type.
Whenever a creature you control of the chosen type enters or attacks, draw a card.

Thought Vessel

Lord of Atlantis

Other Merfolk get +1/+1 and have islandwalk. (They 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}.)

Merrow Commerce

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

Reconnaissance Mission

Whenever a creature you control deals combat damage to a player, you may draw a card.
Cycling {2} ({2}, Discard this card: Draw a card.)

Merrow Reejerey

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

Cursecatcher

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

Sapphire Medallion

Blue spells you cast cost {1} less to cast.

High Tide

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

Seafloor Oracle

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

Aqueous Form

Enchant creature
Enchanted creature can't be blocked.
Whenever enchanted creature attacks, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Mist-Cloaked Herald

Snap

Return target creature to its owner's hand. Untap up to two lands.

Lullmage Mentor

Whenever a spell or ability you control counters a spell, you may create a 1/1 blue Merfolk creature token.
Tap seven untapped Merfolk you control: Counter target spell.

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.

Rogue's Passage

{T}: Add {C}.
{4}, {T}: Target creature can't be blocked this 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.

Cryptic Command

Choose two —
• Counter target spell.
• Return target permanent to its owner's hand.
• Tap all creatures your opponents control.
• Draw a card.

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.

Empress Galina

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

Reef Shaman

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

Merfolk Looter

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.