Secrets of the Golden City

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
Draw two cards. If you have the city's blessing, draw three cards instead.

Island

Jadelight Ranger

When Jadelight Ranger enters the battlefield, 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.)

Forerunner of the Heralds

When Forerunner of the Heralds enters the battlefield, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.
Whenever another Merfolk enters the battlefield under your control, put a +1/+1 counter on Forerunner of the Heralds.

Depths of Desire

Return target creature to its owner's hand. Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Merfolk Mistbinder

Aquatic Incursion

When Aquatic Incursion enters the battlefield, 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.

Mist-Cloaked Herald

Orazca Relic

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
{T}: Add {C}.
{T}, Sacrifice Orazca Relic: You gain 3 life and draw a card. Activate only if you have the city's blessing.

Vineshaper Mystic

When Vineshaper Mystic enters the battlefield, put a +1/+1 counter on each of up to two target Merfolk you control.

Jungleborn Pioneer

When Jungleborn Pioneer enters the battlefield, create a 1/1 blue Merfolk creature token with hexproof. (It can't be the target of spells or abilities your opponents control.)

Crashing Tide

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

Waterknot

Enchant creature
When Waterknot enters the battlefield, tap enchanted creature.
Enchanted creature doesn't untap during its controller's untap step.

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.

Dive Down

Target creature you control gets +0/+3 and gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)

Tishana's Wayfinder

When Tishana's Wayfinder enters the battlefield, 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.)

Shapers of Nature

{3}{G}: Put a +1/+1 counter on target creature.
{2}{U}, Remove a +1/+1 counter from a creature you control: Draw a card.

Storm Sculptor

Storm Sculptor can't be blocked.
When Storm Sculptor enters the battlefield, return a creature you control to its owner's hand.

Negate

River Heralds' Boon

Put a +1/+1 counter on target creature and a +1/+1 counter on up to one target Merfolk.

Seafloor Oracle

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

Headwater Sentries

Siren Stormtamer

Flying
{U}, Sacrifice Siren Stormtamer: Counter target spell or ability that targets you or a creature you control.

Unclaimed Territory

As Unclaimed Territory enters the battlefield, 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.

Overflowing Insight

Entrancing Melody

Gain control of target creature with mana value X.

Forest

Tempest Caller

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

River's Rebuke

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

Deeproot Warrior

Whenever Deeproot Warrior becomes blocked, it gets +1/+1 until end of turn.

Watertrap Weaver

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

Pounce

Target creature you control fights target creature you don't control. (Each deals damage equal to its power to the other.)

Jade Bearer

When Jade Bearer enters the battlefield, put a +1/+1 counter on another target Merfolk you control.

Traveler's Amulet

{1}, Sacrifice Traveler's Amulet: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.

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.)

Herald of Secret Streams

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

Deeproot Champion

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

Naturalize

One With the Wind

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

River Sneak

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

New Horizons

Enchant land
When New Horizons enters the battlefield, put a +1/+1 counter on target creature you control.
Enchanted land has "{T}: Add two mana of any one color."

Admiral's Order

Raid — If you attacked this turn, you may pay {U} rather than pay this spell's mana cost.
Counter target spell.

Strength of the Pack

Put two +1/+1 counters on each creature you control.

Kumena's Speaker

Kumena's Speaker gets +1/+1 as long as you control another Merfolk or an Island.

Blinding Fog

Prevent all damage that would be dealt to creatures this turn. Creatures you control gain hexproof until end of turn. (They can't be the targets of spells or abilities your opponents control.)

Shaper Apprentice

Shaper Apprentice has flying as long as you control another Merfolk.

Sea Legs

Flash
Enchant creature
Enchanted creature gets +0/+2 as long as it's a Pirate. Otherwise, it gets -2/-0.

Spell Pierce

Counter target noncreature spell unless its controller pays {2}.

Cancel

Jade Guardian

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
When Jade Guardian enters the battlefield, put a +1/+1 counter on target Merfolk you control.

Flood of Recollection

Return target instant or sorcery card from your graveyard to your hand. Exile Flood of Recollection.

Siren Lookout

Flying
When Siren Lookout enters the battlefield, 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.)

Merfolk Branchwalker

When Merfolk Branchwalker enters the battlefield, 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.)

Hornswoggle

Counter target creature spell. You create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

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.

Silent Gravestone

Cards in graveyards can't be the targets of spells or abilities.
{4}, {T}: Exile Silent Gravestone and all cards from all graveyards. Draw a card.

Woodland Stream

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

Riverwise Augur

When Riverwise Augur enters the battlefield, draw three cards, then put two cards from your hand on top of your library in any order.

Deeproot Elite

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

Perilous Voyage

Return target nonland permanent you don't control to its owner's hand. If its mana value was 2 or less, scry 2.

Jungle Delver

{3}{G}: Put a +1/+1 counter on Jungle Delver.

Enter the Unknown

Target 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 creature, then put the card back or put it into your graveyard.)
You may play an additional land this turn.

Prying Blade

Equipped creature gets +1/+0.
Whenever equipped creature deals combat damage to a player, create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Pillar of Origins

As Pillar of Origins enters the battlefield, choose a creature type.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type.