Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

When Acidic Slime enters the battlefield, destroy target artifact, enchantment, or land.

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

Counter target spell.

Put a flood counter on target land. That land is an Island in addition to its other types for as long as it has a flood counter on it. If you control a Merfolk, draw a card.

Azorius Chancery enters the battlefield tapped.

When Azorius Chancery enters the battlefield, return a land you control to its owner's hand.

{T}: Add {W}{U}.

{T}: Add {C}.

{1}, {T}, Sacrifice Bant Panorama: Search your library for a basic Forest, Plains, or Island card, put it onto the battlefield tapped, then shuffle.

Whenever a creature you control attacks, you may put a quest counter on Beastmaster Ascension.

As long as Beastmaster Ascension has seven or more quest counters on it, creatures you control get +5/+5.

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.

Botanical Sanctum enters the battlefield tapped unless you control two or fewer other lands.

{T}: Add {G} or {U}.

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.

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

Counter target spell.

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

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

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.)

Flying

When Derevi, Empyrial Tactician enters and whenever a creature you control deals combat damage to a player, you may tap or untap target permanent.

{1}{G}{W}{U}: Put Derevi onto the battlefield from the command zone.

Counter target spell, activated ability, or triggered ability. (Mana abilities can't be targeted.)

Whenever a creature deals combat damage to one of your opponents, its controller may draw a card.

When Eternal Witness enters the battlefield, you may return target card from your graveyard to your hand.

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.

({T}: Add {G}.)

({T}: Add {G}.)

({T}: Add {G}.)

({T}: Add {G}.)

({T}: Add {G}.)

({T}: Add {G}.)

Glacial Fortress enters tapped unless you control a Plains or an Island.

{T}: Add {W} or {U}.

At the beginning of combat on your turn, put a +1/+1 counter on target creature you control. Then if that creature has three or more +1/+1 counters on it, transform Hadana's Climb.

(Transforms from Hadana's Climb.)

{T}: Add one mana of any color.

{1}{G}{U}, {T}: Target creature you control gains flying and gets +X/+X until end of turn, where X is its power.

You may cast Harbinger of the Tides 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 Harbinger of the Tides enters the battlefield, you may return target tapped creature an opponent controls to its owner's hand.

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

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

When Inkfathom Divers enters the battlefield, look at the top four cards of your library, then put them back in any order.

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

+2: Each player draws a card.

-1: Target player draws a card.

-10: Target player mills twenty cards.

+1: Whenever one or more creatures you control deal combat damage to a player this turn, draw a card, then discard a card.

-2: Create a 2/2 blue Illusion creature token with "When this creature becomes the target of a spell, sacrifice it."

-5: Create two tokens that are copies of Jace, Cunning Castaway, except they're not legendary.

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.)

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.

Krosan Verge enters the battlefield tapped.

{T}: Add {C}.

{2}, {T}, Sacrifice Krosan Verge: Search your library for a Forest card and a Plains card, put them onto the battlefield tapped, then shuffle.

Lonely Sandbar enters the battlefield tapped.

{T}: Add {U}.

Cycling {U} ({U}, Discard this card: Draw a card.)

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.)

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

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.)

{T}: Draw a card, then discard a card.

Other Merfolk creatures you control get +1/+1.

{T}: Target Merfolk creature can't be blocked this turn.

Flash

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

Flying

When Merfolk Wayfinder enters the battlefield, 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.

Other Merfolk creatures you control get +1/+1.

Whenever you cast a Merfolk spell, you may tap or untap target permanent.

Changeling (This card is every creature type.)

{X}: Until end of turn, creatures you control have base power and toughness X/X and gain all creature types.

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

({T}: Add {W}.)

({T}: Add {W}.)

As Port Town enters the battlefield, you may reveal a Plains or Island card from your hand. If you don't, Port Town enters the battlefield tapped.

{T}: Add {W} or {U}.

({T}: Add {W} or {U}.)

Prairie Stream enters tapped unless you control two or more basic lands.

Prime Speaker Zegana enters the battlefield with X +1/+1 counters on it, where X is the greatest power among other creatures you control.

When Prime Speaker Zegana enters the battlefield, draw cards equal to its power.

At the beginning of each player's upkeep, that player puts a flood counter on target non-Island land they control of their choice. That land is an Island for as long as it has a flood counter on it.

At the beginning of each end step, if all lands on the battlefield are Islands, remove all flood counters from them.

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)

As Radiant Destiny enters the battlefield, choose a creature type.

Creatures you control of the chosen type get +1/+1. As long as you have the city's blessing, they also have vigilance.

You have no maximum hand size.

{T}: Add {C}.

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

{T}: Rootwater Hunter deals 1 damage to any target.

({T}: Add {G} or {W}.)

Scattered Groves enters the battlefield tapped.

Cycling {2} ({2}, Discard this card: Draw a card.)

Whenever Scroll Thief deals combat damage to a player, draw a card.

Seaside Citadel enters tapped.

{T}: Add {G}, {W}, or {U}.

Sejiri Refuge enters the battlefield tapped.

When Sejiri Refuge enters the battlefield, you gain 1 life.

{T}: Add {W} or {U}.

Flying

You, planeswalkers you control, and other creatures you control have hexproof.

{4}{G}{G}: Put a +1/+1 counter on each creature you control.

{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.

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

When Silvergill Adept enters the battlefield, draw a card.

Simic Growth Chamber enters the battlefield tapped.

When Simic Growth Chamber enters the battlefield, return a land you control to its owner's hand.

{T}: Add {G}{U}.

Flying

Whenever Smuggler's Copter attacks or blocks, you may draw a card. If you do, discard a card.

Crew 1 (Tap any number of creatures you control with total power 1 or more: This Vehicle becomes an artifact creature until end of turn.)

{T}: Add {C}{C}.

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

All lands are Islands in addition to their other types.

Creatures without flying or islandwalk can't attack.

{T}: Target Merfolk creature gets +1/+1 and gains islandwalk until end of turn. (It can't be blocked as long as defending player controls an Island.)

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

Create two 1/1 blue Merfolk Wizard creature tokens.

Tap four untapped Merfolk you control: Return Summon the School from your graveyard to your hand.

{T}: Add {C}.

{T}, Tap an untapped creature you control: Add one mana of any color.

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

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

{1}{W}: Target Merfolk you control gains protection from the color of your choice until end of turn.

Exile up to two target artifacts and/or enchantments.

Basic landcycling {2} ({2}, Discard this card: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.)

+1: Choose up to two target creatures. Until your next turn, whenever either of those creatures deals combat damage, you draw a card.

-2: Tap up to two target nonland permanents. They don't untap during their controller's next untap step.

-7: Draw three cards. You get an emblem with "You may cast spells from your hand without paying their mana costs."

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

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Whenever Thada Adel, Acquisitor deals combat damage to a player, search that player's library for an artifact card and exile it. Then that player shuffles. Until end of turn, you may play that card.

At the beginning of your end step, each opponent loses life equal to the number of tapped creatures you control.

When Tidal Courier enters the battlefield, reveal the top four cards of your library. Put all Merfolk cards revealed this way into your hand and the rest on the bottom of your library in any order.

{3}{U}: Tidal Courier gains flying until end of turn.

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

When Tidebinder Mage enters the battlefield, 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.

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.)

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 the battlefield, draw a card for each creature you control.

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.

As Vanquisher's Banner enters the battlefield, choose a creature type.

Creatures you control of the chosen type get +1/+1.

Whenever you cast a creature spell of the chosen type, draw a card.

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

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

Whenever a permanent you control becomes untapped, Wake Thrasher gets +1/+1 until end of turn.

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