Shielded by Faith

Enchant creature
Enchanted creature has indestructible.
Whenever a creature enters, you may attach Shielded by Faith to that creature.

Tishana, Voice of Thunder

Tishana, Voice of Thunder's power and toughness are each equal to the number of cards in your hand.
You have no maximum hand size.
When Tishana enters, draw a card for each creature you control.

Unexpected Results

Shuffle your library, then reveal the top card. If it's a nonland card, you may cast it without paying its mana cost. If it's a land card, you may put it onto the battlefield and return Unexpected Results to its owner's hand.

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.)

Counterspell

Mirari's Wake

Creatures you control get +1/+1.
Whenever you tap a land for mana, add one mana of any type that land produced.

Cold-Eyed Selkie

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever Cold-Eyed Selkie deals combat damage to a player, you may draw that many cards.

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Scattered Groves

({T}: Add {G} or {W}.)
Scattered Groves enters tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

Judge of Currents

Whenever a Merfolk you control becomes tapped, you may gain 1 life.

Rootwater Shaman

You may cast Aura spells with enchant creature as though they had flash.

Celestial Mantle

Enchant creature
Enchanted creature gets +3/+3.
Whenever enchanted creature deals combat damage to a player, double its controller's life total.

Bear Umbra

Enchant creature
Enchanted creature gets +2/+2 and has "Whenever this creature attacks, untap all lands you control."
Umbra armor (If enchanted creature would be destroyed, instead remove all damage from it and destroy this Aura.)

Rejuvenating Springs

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

Botanical Sanctum

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

Daybreak Coronet

Enchant creature with another Aura attached to it
Enchanted creature gets +3/+3 and has first strike, vigilance, and lifelink. (Damage dealt by the creature also causes its controller to gain that much life.)

All That Glitters

Enchant creature
Enchanted creature gets +1/+1 for each artifact and/or enchantment you control.

Mantle of the Ancients

Enchant creature you control
When Mantle of the Ancients enters, return any number of target Aura and/or Equipment cards from your graveyard to the battlefield attached to enchanted creature.
Enchanted creature gets +1/+1 for each Aura and Equipment attached to it.

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Forest

Irrigated Farmland

({T}: Add {W} or {U}.)
Irrigated Farmland enters tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

Adrix and Nev, Twincasters

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
If one or more tokens would be created under your control, twice that many of those tokens are created instead.

Plains

As Foretold

At the beginning of your upkeep, put a time counter on As Foretold.
Once each turn, you may pay {0} rather than pay the mana cost for a spell you cast with mana value X or less, where X is the number of time counters on As Foretold.

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.)

Skyblade's Boon

Enchant creature
Enchanted creature gets +1/+1 and has flying.
{2}{W}: Return Skyblade's Boon to its owner's hand. Activate only if Skyblade's Boon is on the battlefield or in your graveyard.

Enchantress's Presence

Whenever you cast an enchantment spell, draw a card.

Canopy Vista

({T}: Add {G} or {W}.)
Canopy Vista enters tapped unless you control two or more basic lands.

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}.

Tuvasa the Sunlit

Tuvasa the Sunlit gets +1/+1 for each enchantment you control.
Whenever you cast your first enchantment spell each turn, draw a card.

Sunpetal Grove

Sunpetal Grove enters tapped unless you control a Forest or a Plains.
{T}: Add {G} or {W}.

Kindred Boon

As Kindred Boon enters, choose a creature type.
{1}{W}: Put a divinity counter on target creature you control of the chosen type.
Each creature you control with a divinity counter on it has indestructible.

Privileged Position

({G/W} can be paid with either {G} or {W}.)
Other permanents you control have hexproof. (They can't be the targets of spells or abilities your opponents control.)

Seafloor Oracle

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

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Razorverge Thicket

Razorverge Thicket enters tapped unless you control two or fewer other lands.
{T}: Add {G} or {W}.

Deeproot Champion

Whenever you cast a noncreature spell, put a +1/+1 counter on Deeproot Champion.

One With the Wind

Enchant creature
Enchanted creature gets +2/+2 and has flying.

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.")

Breeding Pool

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

Rhystic Study

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

Temple of the False God

{T}: Add {C}{C}. Activate only if you control five or more lands.

Port Town

As Port Town enters, you may reveal a Plains or Island card from your hand. If you don't, Port Town enters tapped.
{T}: Add {W} or {U}.

Hinterland Harbor

Hinterland Harbor enters tapped unless you control a Forest or an Island.
{T}: Add {G} or {U}.

Spirit Mantle

Enchant creature
Enchanted creature gets +1/+1 and has protection from creatures.

Asceticism

Creatures you control have hexproof.
{1}{G}: Regenerate target creature. (The next time it would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Homeward Path

{T}: Add {C}.
{T}: Each player gains control of all creatures they own.

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 Sovereign

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

Overgrown Farmland

Overgrown Farmland enters tapped unless you control two or more other lands.
{T}: Add {G} or {W}.

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.

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.

Windswept Heath

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

Temple Garden

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

Bountiful Promenade

Bountiful Promenade enters tapped unless you have two or more opponents.
{T}: Add {G} or {W}.

Mask

Enchant permanent
Totem armor (If enchanted permanent would be destroyed, instead remove all damage from it and destroy this Aura.)

Hallowed Fountain

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

Island

Lord of Atlantis

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

Timely Ward

You may cast Timely Ward as though it had flash if it targets a commander.
Enchant creature
Enchanted creature has indestructible.

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.)

Sterling Grove

Other enchantments you control have shroud. (They can't be the targets of spells or abilities.)
{1}, Sacrifice Sterling Grove: Search your library for an enchantment card, reveal it, then shuffle and put that card on top.

Merfolk

Merrow Reejerey

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

Spider Umbra

Enchant creature
Enchanted creature gets +1/+1 and has reach. (It can block creatures with flying.)
Umbra armor (If enchanted creature would be destroyed, instead remove all damage from it and destroy this Aura.)

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Seaside Citadel

Seaside Citadel enters tapped.
{T}: Add {G}, {W}, or {U}.

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.

Empress Galina

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

Herald of Secret Streams

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

On Serra's Wings

Enchant creature
Enchanted creature is legendary, gets +1/+1, and has flying, vigilance, and lifelink.

Sol Ring

Deeproot Elite

Whenever another Merfolk you control enters, put a +1/+1 counter on target Merfolk you control.

Ethereal Armor

Enchant creature
Enchanted creature gets +1/+1 for each enchantment you control and has first strike.

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.

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}.)

Vorel of the Hull Clade

{G}{U}, {T}: Double the number of each kind of counter on target artifact, creature, or land.

Thassa, God of the Sea

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)
At the beginning of your upkeep, scry 1.
{1}{U}: Target creature you control can't be blocked this turn.

Spreading Seas

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

Sea of Clouds

Sea of Clouds enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Austere Command

Choose two —
• Destroy all artifacts.
• Destroy all enchantments.
• Destroy all creatures with mana value 3 or less.
• Destroy all creatures with mana value 4 or greater.

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.

Reliquary Tower

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

Flooded Strand

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

Prairie Stream

({T}: Add {W} or {U}.)
Prairie Stream enters tapped unless you control two or more basic lands.

Elemental

Seachrome Coast

Seachrome Coast enters tapped unless you control two or fewer other lands.
{T}: Add {W} or {U}.

Merfolk Mistbinder

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.

Wanderwine Hub

As Wanderwine Hub enters, you may reveal a Merfolk card from your hand. If you don't, Wanderwine Hub enters tapped.
{T}: Add {W} or {U}.

Chromatic Lantern

Lands you control have "{T}: Add one mana of any color."
{T}: Add one mana of any color.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Estrid, the Masked

+2: Untap each enchanted permanent you control.
−1: Create a white Aura enchantment token named Mask attached to another target permanent. The token has enchant permanent and umbra armor.
−7: Mill seven cards. Return all non-Aura enchantment cards from your graveyard to the battlefield, then do the same for Aura cards.
Estrid, the Masked can be your commander.

Glacial Fortress

Glacial Fortress enters tapped unless you control a Plains or an Island.
{T}: Add {W} or {U}.

Copy

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

Deserted Beach

Deserted Beach enters tapped unless you control two or more other lands.
{T}: Add {W} or {U}.

Deeproot Pilgrimage

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

Command Tower

Expedition Map

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

Thassa's Oracle

When Thassa's Oracle enters, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Ancestral Mask

Enchant creature
Enchanted creature gets +2/+2 for each other enchantment on the battlefield.

True-Name Nemesis

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