Myriad Landscape

Myriad Landscape enters tapped.
{T}: Add {C}.
{2}, {T}, Sacrifice Myriad Landscape: Search your library for up to two basic land cards that share a land type, put them onto the battlefield tapped, then shuffle.

1 deck added

Arcane Denial

Counter target spell. Its controller may draw up to two cards at the beginning of the next turn's upkeep.
You draw a card at the beginning of the next turn's upkeep.

1 deck removed

Deeproot Wayfinder

Whenever Deeproot Wayfinder deals combat damage to a player or battle, surveil 1, then you may return a land card from your graveyard to the battlefield tapped. (To surveil 1, look at the top card of your library. You may put that card into your graveyard.)

Vorel of the Hull Clade

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

Remove multiple decks removed

Arcane Signet

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

Don't Have

Frog Lizard

Rapid Hybridization

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

Mosswort Bridge

Hideaway 4 (When this land enters, look at the top four cards of your library, exile one face down, then put the rest on the bottom in a random order.)
Mosswort Bridge enters tapped.
{T}: Add {G}.
{G}, {T}: You may play the exiled card without paying its mana cost if creatures you control have total power 10 or greater.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Have

{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.)

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.)

Temple of the False God

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

Not in another deck

True-Name Nemesis

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

Singer of Swift Rivers

Flash
When Singer of Swift Rivers enters, put a shield counter on another target creature you control. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
You may cast Merfolk spells as though they had flash.

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.

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.

Ripples of Potential

Proliferate, then choose any number of permanents you control that had a counter put on them this way. Those permanents phase out. (To proliferate, choose any number of permanents and/or players, then give each another counter of each kind already there. Treat phased-out permanents and anything attached to them as though they don't exist until their controller's next turn.)

Seafloor Oracle

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

Merfolk Sovereign

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

Beast

Commander's Sphere

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

Multiple decks removed

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.

Island

Wonder

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

Propaganda

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

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.)

Jadelight Ranger

When Jadelight Ranger enters, it explores, then it explores again. (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. Then repeat this process.)

Path of Ancestry

Path of Ancestry 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.)

Merfolk Mistbinder

Explore

You may play an additional land this turn.
Draw a card.

Hardened Scales

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

Rivendell

Rivendell enters tapped unless you control a legendary creature.
{T}: Add {U}.
{1}{U}, {T}: Scry 2. Activate only if you control a legendary creature.

Patchwork Banner

As Patchwork Banner enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
{T}: Add one mana of any color.

Beast Within

Destroy target permanent. Its controller creates a 3/3 green Beast creature token.

Rogue's Passage

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

Merrow Reejerey

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

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.

Topography Tracker

When Topography Tracker 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.")
If a creature you control would explore, instead it explores, then it explores again.

Silvergill Adept

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

Thriving Grove

Thriving Grove enters tapped. As it enters, choose a color other than green.
{T}: Add {G} or one mana of the chosen color.

Marina Vendrell's Grimoire

When Marina Vendrell's Grimoire enters, if you cast it, draw five cards.
You have no maximum hand size and don't lose the game for having 0 or less life.
Whenever you gain life, draw that many cards.
Whenever you lose life, discard that many cards. Then if you have no cards in hand, you lose the game.

Return to Nature

Choose one —
• Destroy target artifact.
• Destroy target enchantment.
• Exile target card from a graveyard.

Merfolk Trickster

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

Scion of the Deep

Reliquary Tower

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

Herald of Secret Streams

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

Multiple decks added

Raise the Palisade

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

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.

Thieving Skydiver

Kicker {X}. X can't be 0. (You may pay an additional {X} as you cast this spell.)
Flying
When Thieving Skydiver enters, if it was kicked, gain control of target artifact with mana value X or less. If that artifact is an Equipment, attach it to Thieving Skydiver.

Thriving Isle

Thriving Isle enters tapped. As it enters, choose a color other than blue.
{T}: Add {U} or one mana of the chosen color.

Concordant Crossroads

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.

Herald's Horn

As Herald's Horn enters, choose a creature type.
Creature spells you cast of the chosen type cost {1} less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

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}.

Filter Out

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

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.

Deeproot Historian

Merfolk and Druid cards in your graveyard have retrace. (You may cast cards with retrace from your graveyard by discarding a land card in addition to paying their other costs.)

Merfolk

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

Temporal Trespass

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Take an extra turn after this one. Exile Temporal Trespass.

Multiple decks and available 

Banner of Kinship

As this artifact enters, choose a creature type. This artifact enters with a fellowship counter on it for each creature you control of the chosen type.
Creatures you control of the chosen type get +1/+1 for each fellowship counter on this artifact.

Floodpits Drowner

Flash
Vigilance
When Floodpits Drowner enters, tap target creature an opponent controls and put a stun counter on it.
{1}{U}, {T}: Shuffle Floodpits Drowner and target creature with a stun counter on it into their owners' libraries.

Evolution Sage

Landfall — Whenever a land you control enters, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

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.

Forest

Alchemist's Refuge

{T}: Add {C}.
{G}{U}, {T}: You may cast spells this turn as though they had flash.

Journey to the Oracle

You may put any number of land cards from your hand onto the battlefield. Then if you control eight or more lands, you may discard a card. If you do, return Journey to the Oracle to its owner's hand.

Jadzi, Oracle of Arcavios

Discard a card: Return Jadzi, Oracle of Arcavios to its owner's hand.
Magecraft — Whenever you cast or copy an instant or sorcery spell, reveal the top card of your library. If it's a nonland card, you may cast it by paying {1} rather than paying its mana cost. If it's a land card, put it onto the battlefield.

Jadzi, Oracle of Arcavios // Journey to the Oracle

Karn's Bastion

{T}: Add {C}.
{4}, {T}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

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.")

Vodalian Hexcatcher

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

Kiora, the Rising Tide

When Kiora enters, draw two cards, then discard two cards.
Threshold — Whenever Kiora attacks, if there are seven or more cards in your graveyard, you may create Scion of the Deep, a legendary 8/8 blue Octopus creature token.

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.)

Secluded Courtyard

As this land 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 or activate an ability of a creature source of the chosen type.

The Reality Chip

You may look at the top card of your library any time.
As long as The Reality Chip is attached to a creature, you may play lands and cast spells from the top of your library.
Reconfigure {2}{U} ({2}{U}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn't a creature.)

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.

Mutational Advantage

Permanents you control with counters on them gain hexproof and indestructible until end of turn. Prevent all damage that would be dealt to those permanents this turn. Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Bred for the Hunt

Whenever a creature you control with a +1/+1 counter on it deals combat damage to a player, you may draw a card.

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}.

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.

Aetherize

Return all attacking creatures to their owner's hand.

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.

Benthic Biomancer

{1}{U}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.)
Whenever one or more +1/+1 counters are put on Benthic Biomancer, draw a card, then discard a card.

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.

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.

Simic Growth Chamber

Simic Growth Chamber enters tapped.
When Simic Growth Chamber enters, return a land you control to its owner's hand.
{T}: Add {G}{U}.

Ruinous Intrusion

Exile target artifact or enchantment. Put X +1/+1 counters on target creature you control, where X is the mana value of the permanent exiled this way.

Wave Goodbye

Return each creature without a +1/+1 counter on it to its owner's hand.

Copy

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

Command Tower

Nature's Lore

Search your library for a Forest card, put that card onto the battlefield, then shuffle.

Fierce Guardianship

If you control a commander, you may cast this spell without paying its mana cost.
Counter target noncreature spell.

Branching Evolution

If one or more +1/+1 counters would be put on a creature you control, twice that many +1/+1 counters are put on that creature instead.

Zegana, Utopian Speaker

When Zegana, Utopian Speaker enters, if you control another creature with a +1/+1 counter on it, draw a card.
{4}{G}{U}: Adapt 4. (If this creature has no +1/+1 counters on it, put four +1/+1 counters on it.)
Each creature you control with a +1/+1 counter on it has trample.

Kodama's Reach

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Fangs of Kalonia

Put a +1/+1 counter on target creature you control, then double the number of +1/+1 counters on each creature that had a +1/+1 counter put on it this way.
Overload {4}{G}{G} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Prime Speaker Zegana

Prime Speaker Zegana enters with X +1/+1 counters on it, where X is the greatest power among other creatures you control.
When Prime Speaker Zegana enters, draw cards equal to its power.

Realmwalker

Changeling (This card is every creature type.)
As Realmwalker enters, choose a creature type.
You may look at the top card of your library any time.
You may cast creature spells of the chosen type from the top of your library.

Thought Vessel

River's Rebuke

Return all nonland permanents target player controls to their owner's hand.

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}.)

Deeproot Elite

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