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.

Inscribed Tablet

{1}, {T}, Sacrifice this artifact: Reveal the top five cards of your library. Put a land card from among them into your hand and the rest on the bottom of your library in a random order. If you didn't put a card into your hand this way, draw a card.

Wizard Class

(Gain the next level as a sorcery to add its ability.)
You have no maximum hand size.
{2}{U}: Level 2
When this Class becomes level 2, draw two cards.
{4}{U}: Level 3
Whenever you draw a card, put a +1/+1 counter on target creature you control.

Crystal Grotto

When this land enters, scry 1.
{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Jace, Arcane Strategist

Whenever you draw your second card each turn, put a +1/+1 counter on target creature you control.
+1: Draw a card.
−7: Creatures you control can't be blocked this turn.

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.)

Merfolk Trickster

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

Force of Negation

If it's not your turn, you may exile a blue card from your hand rather than pay this spell's mana cost.
Counter target noncreature spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Curate

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.)
Draw a card.

Silvergill Adept

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

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.

Tide Shaper

Kicker {1} (You may pay an additional {1} as you cast this spell.)
When this creature enters, if it was kicked, target land becomes an Island for as long as this creature remains on the battlefield.
This creature gets +1/+1 as long as an opponent controls an Island.

Urza's Incubator

As this artifact enters, choose a creature type.
Creature spells of the chosen type cost {2} less to cast.

Merfolk Looter

Demolition Field

{T}: Add {C}.
{2}, {T}, Sacrifice this land: Destroy target nonbasic land an opponent controls. That land's controller may search their library for a basic land card, put it onto the battlefield, then shuffle. You may search your library for a basic land card, put it onto the battlefield, then shuffle.

Unsubstantiate

Return target spell or creature to its owner's hand.

Rishadan Dockhand

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
{1}, {T}: Tap target land.

Traveler's Amulet

{1}, Sacrifice this artifact: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.

Tidal Warrior

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

River Herald Scout

When this creature 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.)

River Sneak

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

Icy Prison

When this enchantment enters, exile target creature.
At the beginning of your upkeep, sacrifice this enchantment unless any player pays {3}.
When this enchantment leaves the battlefield, return the exiled card to the battlefield under its owner's control.

Island

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.

Skyline Cascade

This land enters tapped.
When this land enters, target creature an opponent controls doesn't untap during its controller's next untap step.
{T}: Add {U}.

Deeproot Pilgrimage

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

Aquatic Incursion

When this enchantment 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.

Gray Harbor Merfolk

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

Tempest Caller

When this creature enters, tap all creatures target opponent controls.

Vodalian Hexcatcher

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

Merrow Commerce

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

Spreading Seas

Enchant land
When this Aura enters, draw a card.
Enchanted land is an Island.

Counterspell

High Tide

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

Watertrap Weaver

When this creature enters, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

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.

Triton Shorestalker

Caged Sun

As this artifact enters, choose a color.
Creatures you control of the chosen color get +1/+1.
Whenever a land's ability causes you to add one or more mana of the chosen color, add one additional mana of that color.

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.

Merrow Reejerey

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

Nyx Lotus

Nyx Lotus enters tapped.
{T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)

Svyelun of Sea and Sky

Svyelun 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}.)

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.

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.

Galestrike

Return target tapped creature to its owner's hand.
Draw a card.

Shaper Apprentice

This creature has flying as long as you control another Merfolk.

Siren's Call

Cast this spell only during an opponent's turn, before attackers are declared.
Creatures the active player controls attack this turn if able.
At the beginning of the next end step, destroy all non-Wall creatures that player controls that didn't attack this turn. Ignore this effect for each creature the player didn't control continuously since the beginning of the turn.

Filter Out

Return all noncreature, nonland permanents to their owners' hands.

Lord of Atlantis

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

Slip Out the Back

Put a +1/+1 counter on target creature. It phases out. (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

Polymorph

Destroy target creature. It can't be regenerated. Its controller reveals cards from the top of their library until they reveal a creature card. The player puts that card onto the battlefield, then shuffles all other cards revealed this way into their library.

Merfolk Sovereign

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

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.)

Warped Landscape

{T}: Add {C}.
{2}, {T}, Sacrifice this land: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Ordeal of Thassa

Enchant creature
Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice this Aura.
When you sacrifice this Aura, draw two cards.

Tideshaper Mystic

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

Teferi's Time Twist

Exile target permanent you control. Return that card to the battlefield under its owner's control at the beginning of the next end step. If it enters as a creature, it enters with an additional +1/+1 counter on it.

Path of Ancestry

This land enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

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.

Tidebinder Mage

When this creature 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 this creature.

Blighted Cataract

{T}: Add {C}.
{5}{U}, {T}, Sacrifice this land: Draw two cards.

Merfolk Wayfinder

Flying
When this creature 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.

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Curiosity

Enchant creature
Whenever enchanted creature deals damage to an opponent, you may draw a card.

Cleric of Chill Depths

Whenever this creature blocks a creature, that creature doesn't untap during its controller's next untap step.

Merrow Harbinger

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
When this creature enters, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.

Seafloor Oracle

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

Mist-Cloaked Herald

Rapid Hybridization

Destroy target creature. It can't be regenerated. That creature's controller creates a 3/3 green Frog Lizard creature token.

Pongify

Destroy target creature. It can't be regenerated. Its controller creates a 3/3 green Ape creature token.