Thrasios, Triton Hero

{4}: Scry 1, then reveal the top card of your library. If it's a land card, put it onto the battlefield tapped. Otherwise, draw a card.
Partner (You can have two commanders if both have partner.)

Hidden Cataract

Hidden Cataract enters tapped.
{T}: Add {U}.
{4}{U}, {T}, Sacrifice Hidden Cataract: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Hakbal of the Surging Soul

At the beginning of combat on your turn, each Merfolk creature you control 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 the exploring creature, then put the card back or put it into your graveyard.)
Whenever Hakbal of the Surging Soul attacks, you may put a land card from your hand onto the battlefield. If you don't, draw a card.

Deepfathom Echo

At the beginning of combat on your turn, Deepfathom Echo explores. Then you may have it become a copy of another creature you control until end of turn. (To have this creature explore, 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.)

Eaten by Piranhas

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Enchanted creature loses all abilities and is a black Skeleton creature with base power and toughness 1/1. (It loses all other colors, card types, and creature types.)

Rhystic Study

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

Nicanzil, Current Conductor

Whenever a creature you control explores a land card, you may put a land card from your hand onto the battlefield tapped.
Whenever a creature you control explores a nonland card, put a +1/+1 counter on Nicanzil, Current Conductor.

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.")

Ozolith, the Shattered Spire

If one or more +1/+1 counters would be put on an artifact or creature you control, that many plus one +1/+1 counters are put on it instead.
{1}{G}, {T}: Put a +1/+1 counter on target artifact or creature you control. Activate only as a sorcery.
Cycling {2} ({2}, Discard this card: Draw a card.)

Volatile Fault

{T}: Add {C}.
{1}, {T}, Sacrifice Volatile Fault: Destroy target nonbasic land an opponent controls. That player may search their library for a basic land card, put it onto the battlefield, then shuffle. You create a Treasure token.

Misty Rainforest

{T}, Pay 1 life, Sacrifice Misty Rainforest: Search your library for a Forest or Island card, put it onto the battlefield, then shuffle.

Tempest Caller

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

Merfolk Coralsmith

{1}: Merfolk Coralsmith gets +1/-1 until end of turn.
When Merfolk Coralsmith dies, scry 2.

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.)

Breeding Pool

({T}: Add {G} or {U}.)
As Breeding Pool enters, you may pay 2 life. If you don't, it enters tapped.

River Herald Scout

When River Herald Scout 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.)

Tangled Islet

({T}: Add {G} or {U}.)
Tangled Islet enters tapped.

Dramatic Reversal

Untap all nonland permanents you control.

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.

Raise the Palisade

Choose a creature type. Return all creatures that aren't of the chosen type to their owners' hands.

Merfolk

Hexproof (This creature can't be the target of spells or abilities your opponents control.)

For the Ancestors

Choose a creature type. Look at the top six cards of your library. You may reveal any number of cards of the chosen type from among them and put the revealed cards into your hand. Put the rest on the bottom of your library in a random order.
Flashback {3}{G} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

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.

Spelunking

When Spelunking enters, draw a card, then you may put a land card from your hand onto the battlefield. If you put a Cave onto the battlefield this way, you gain 4 life.
Lands you control enter untapped.

Succumb to the Cold

Tap one or two target creatures an opponent controls. Put a stun counter on each of them. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Vineglimmer Snarl

As Vineglimmer Snarl enters, you may reveal a Forest or Island card from your hand. If you don't, Vineglimmer Snarl enters tapped.
{T}: Add {G} or {U}.

Rimewood Falls

({T}: Add {G} or {U}.)
Rimewood Falls enters tapped.

Abjure

As an additional cost to cast this spell, sacrifice a blue permanent.
Counter target spell.

Forest

Rejuvenating Springs

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

Promising Vein

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

Kumena, Tyrant of Orazca

Tap another untapped Merfolk you control: Kumena, Tyrant of Orazca can't be blocked this turn.
Tap three untapped Merfolk you control: Draw a card.
Tap five untapped Merfolk you control: Put a +1/+1 counter on each Merfolk you control.

Woodland Stream

Woodland Stream enters tapped.
{T}: Add {G} or {U}.

Coral Trickster

Morph {U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Coral Trickster is turned face up, you may tap or untap target permanent.

Island

Doubling Season

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.
If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead.

Decisive Denial

Choose one —
• Target creature you control fights target creature you don't control. (Each deals damage equal to its power to the other.)
• Counter target noncreature spell unless its controller pays {3}.

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.

Yavimaya Coast

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

Hidden Nursery

Hidden Nursery enters tapped.
{T}: Add {G}.
{4}{G}, {T}, Sacrifice Hidden Nursery: Discover 4. Activate only as a sorcery. (Exile cards from the top of your library until you exile a nonland card with mana value 4 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)

Exploration

You may play an additional land on each of your turns.

Danny Pink

Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
Creatures you control have "Whenever one or more counters are put on this creature for the first time each turn, draw a card."

Cenote Scout

When Cenote Scout 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.)

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.)

Cyclonic Rift

Return target nonland permanent you don't control to its owner's hand.
Overload {6}{U} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Riptide Pilferer

Whenever Riptide Pilferer deals combat damage to a player, that player discards a card.
Morph {U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Lord of Atlantis

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

Roaming Throne

Ward {2}
As Roaming Throne enters, choose a creature type.
Roaming Throne is the chosen type in addition to its other types.
If a triggered ability of another creature you control of the chosen type triggers, it triggers an additional time.

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.

Copy

(This token can be used to represent a token that's a copy of a permanent.)

Overwhelming Stampede

Until end of turn, creatures you control gain trample and get +X/+X, where X is the greatest power among creatures you control.

Botanical Sanctum

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

Vodalian Hexcatcher

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

Augur of Bolas

When Augur of Bolas enters, look at the top three cards of your library. You may reveal an instant or sorcery card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Zoetic Glyph

Enchant artifact
Enchanted artifact is a Golem creature with base power and toughness 5/4 in addition to its other types.
When Zoetic Glyph is put into a graveyard from the battlefield, discover 3.

Triton Cavalry

Heroic — Whenever you cast a spell that targets Triton Cavalry, you may return target enchantment to its owner's hand.

Dreamroot Cascade

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

Waterwind Scout

Flying
When Waterwind Scout enters, create a Map token. (It's an artifact with "{1}, {T}, Sacrifice this artifact: Target creature you control explores. Activate only as a sorcery.")

Deeproot Pilgrimage

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

Breaking Wave

You may cast Breaking Wave as though it had flash if you pay {2} more to cast it. (You may cast it any time you could cast an instant.)
Simultaneously untap all tapped creatures and tap all untapped creatures.

Levitation

Zephyr Boots

Equipped creature has flying.
Whenever equipped creature deals combat damage to a player, draw a card, then discard a card.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Herald of Secret Streams

Creatures you control with +1/+1 counters on them can't be blocked.

Salvager of Secrets

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

Merrow Commerce

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

Wavecrash Triton

Heroic — Whenever you cast a spell that targets Wavecrash Triton, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Tanglepool Bridge

Tanglepool Bridge enters tapped.
Indestructible
{T}: Add {G} or {U}.

Cephalid Coliseum

{T}: Add {U}. Cephalid Coliseum deals 1 damage to you.
Threshold — {U}, {T}, Sacrifice Cephalid Coliseum: Target player draws three cards, then discards three cards. Activate only if seven or more cards are in your graveyard.

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.

Tishana's Tidebinder

Flash
When Tishana's Tidebinder enters, counter up to one target activated or triggered ability. If an ability of an artifact, creature, or planeswalker is countered this way, that permanent loses all abilities for as long as Tishana's Tidebinder remains on the battlefield. (Mana abilities can't be targeted.)

Jadelight Spelunker

When Jadelight Spelunker enters, it explores X times. (To have it explore, 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 that creature, then put the card back or put it into your graveyard.)

Merfolk Cave-Diver

Whenever a creature you control explores, Merfolk Cave-Diver gets +1/+0 until end of turn and can't be blocked this turn.

Restless Vinestalk

Restless Vinestalk enters tapped.
{T}: Add {G} or {U}.
{3}{G}{U}: Until end of turn, Restless Vinestalk becomes a 5/5 green and blue Plant creature with trample. It's still a land.
Whenever Restless Vinestalk attacks, up to one other target creature has base power and toughness 3/3 until end of turn.

Thornwood Falls

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {G} or {U}.

Temple of Mystery

This land enters tapped.
When this land enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
{T}: Add {G} or {U}.

Treasure

{T}, Sacrifice this token: Add one mana of any color.

{1}, {T}, Sacrifice this artifact: Target creature you control explores. Activate only as a sorcery. (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 that creature, then put the card back or put it into your graveyard.)

Vitalize

Deepwater Hypnotist

Inspired — Whenever Deepwater Hypnotist becomes untapped, target creature an opponent controls gets -3/-0 until end of turn.

Wonder

Flying
As long as Wonder is in your graveyard and you control an Island, creatures you control have flying.

Lumbering Falls

Lumbering Falls enters tapped.
{T}: Add {G} or {U}.
{2}{G}{U}: Lumbering Falls becomes a 3/3 green and blue Elemental creature with hexproof until end of turn. It's still a land.

Tatyova, Benthic Druid

Landfall — Whenever a land you control enters, you gain 1 life and draw a card.

Seeker of Sunlight

{2}{G}: Seeker of Sunlight explores. Activate only as a sorcery. (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.)

Quest for Renewal

Whenever a creature you control becomes tapped, you may put a quest counter on Quest for Renewal.
As long as there are four or more quest counters on Quest for Renewal, untap all creatures you control during each other player's untap step.

Alandra, Sky Dreamer

Whenever you draw your second card each turn, create a 2/2 blue Drake creature token with flying.
Whenever you draw your fifth card each turn, Alandra, Sky Dreamer and Drakes you control each get +X/+X until end of turn, where X is the number of cards in your hand.

Quandrix Campus

Quandrix Campus enters tapped.
{T}: Add {G} or {U}.
{4}, {T}: Scry 1.

Library Larcenist

Whenever Library Larcenist attacks, draw a card.

River Herald Guide

Vigilance
When River Herald Guide 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.)

Captivating Cave

{T}: Add {C}.
{1}, {T}: Add one mana of any color.
{4}, {T}, Sacrifice Captivating Cave: Put two +1/+1 counters on target creature. Activate only as a sorcery.

Minor Misstep

Counter target spell with mana value 1 or less.

Drake

Urban Evolution

Draw three cards. You may play an additional land this turn.

Pit of Offerings

Pit of Offerings enters tapped.
When Pit of Offerings enters, exile up to three target cards from graveyards.
{T}: Add {C}.
{T}: Add one mana of any of the exiled cards' colors.