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.

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

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

{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.

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.

Draw three cards, then put two cards from your hand on top of your library in any order.

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

As Breeding Pool enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

As Cavern of Souls 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, and that spell can't be countered.

Imprint -- When Chrome Mox enters the battlefield, you may exile a nonartifact, nonland card from your hand.

{T}: Add one mana of any of the exiled card's colors.

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 {C}.

{T}, Sacrifice Command Beacon: Put your commander into your hand from the command zone.

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

Counter target spell.

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

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.")

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.)

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.)

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.

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.

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

Counter target noncreature spell.

Counter target instant or sorcery spell unless its controller pays {1}.

Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

If it's not your turn, you may exile a blue card from your hand rather than pay this spell's mana cost.

Counter target noncreature spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

If it's not your turn, you may exile a green card from your hand rather than pay this spell's mana cost.

Destroy up to two target artifacts and/or enchantments.

You may pay 1 life and exile a blue card from your hand rather than pay this spell's mana cost.

Counter target spell.

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} for each creature you control.

Draw a card. You may put a land card from your hand onto the battlefield.

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.

Search your library for up to X basic land cards, where X is the number of tapped creatures you control, put those cards onto the battlefield tapped, then shuffle.

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

As Herald's Horn enters the battlefield, 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.

Permanents you control gain hexproof and indestructible until end of turn.

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.

Draw a card for each creature you control with a +1/+1 counter on it. Those creatures gain indestructible until end of turn. (Damage and effects that say "destroy" don't destroy them.)

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.)

{T}: Untap another target permanent.

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.

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

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.

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

Whenever a spell or ability you control counters a spell, you may create a 1/1 blue Merfolk creature token.

Tap seven untapped Merfolk you control: Counter target spell.

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

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

({U/P} can be paid with either {U} or 2 life.)

Counter target spell with mana value 1.

Flying

When Merfolk Skydiver enters the battlefield, put a +1/+1 counter on target creature you control.

{3}{G}{U}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

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.

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

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

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

{T}: Add {U}.

{U}, {T}: Untap target legendary permanent.

Mist-Cloaked Herald can't be blocked.

Sacrifice Mistcaller: Until end of turn, if a nontoken creature would enter the battlefield and it wasn't cast, exile it instead.

If Mox Diamond would enter the battlefield, you may discard a land card instead. If you do, put Mox Diamond onto the battlefield. If you don't, put it into its owner's graveyard.

{T}: Add one mana of any color.

Metalcraft -- {T}: Add one mana of any color. Activate only if you control three or more artifacts.

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)

Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

This spell costs {2} less to cast if it targets a blue spell.

Counter target spell unless its controller pays {3}.

Each opponent can't draw more than one card each turn.

-2: Look at the top four cards of your library. You may reveal a noncreature, nonland card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

{T}: Add {C}.

{2}, {T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)

+2: Create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this artifact: You gain 3 life.")

+1: Target artifact or creature loses all abilities and becomes a green Elk creature with base power and toughness 3/3.

-5: Exchange control of target artifact or creature you control and target creature an opponent controls with power 3 or less.

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.)

Counter target spell.

At the beginning of your next upkeep, pay {3}{U}{U}. If you don't, you lose the game.

Changeling (This card is every creature type.)

As Realmwalker enters the battlefield, 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.

As Reflections of Littjara enters the battlefield, choose a creature type.

Whenever you cast a spell of the chosen type, copy that spell. (A copy of a permanent spell becomes a token.)

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

River Sneak can't be blocked.

Whenever another Merfolk enters the battlefield under your control, River Sneak gets +1/+1 until end of turn.

Whenever Saprazzan Heir becomes blocked, you may draw three cards.

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

Untap all permanents you control during each other player's untap step.

{1}: Look at the top three cards of your library, then put them back in any order.

{T}: Draw a card, then put Sensei's Divining Top on top of its owner's library.

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

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.

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}.)

Counter target enchantment, instant, or sorcery spell. Its controller creates a 2/2 blue Bird creature token with flying.

{T}: Add {C}.

{T}: Add {G} or {U}. Talisman of Curiosity deals 1 damage to you.

Landfall -- Whenever a land enters the battlefield under your control, you gain 1 life and draw a card.

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.

This spell costs {X} less to cast, where X is the greatest power among creatures you control.

{T}: Add {G}{G}. You gain 2 life.

Whenever a nontoken creature enters the battlefield under your control, put a +1/+1 counter on it and draw a card.

Whenever a creature you control leaves the battlefield, if it had counters on it, put those counters on The Ozolith.

At the beginning of combat on your turn, if The Ozolith has counters on it, you may move all counters from The Ozolith onto target creature.

Kicker {X}. X can't be 0. (You may pay an additional {X} as you cast this spell.)

Flying

When Thieving Skydiver enters the battlefield, 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.

Kicker {1} (You may pay an additional {1} as you cast this spell.)

When Tide Shaper enters the battlefield, if it was kicked, target land becomes an Island for as long as Tide Shaper remains on the battlefield.

Tide Shaper gets +1/+1 as long as an opponent controls an Island.

Each player shuffles their hand and graveyard into their library, then draws seven cards. (Then put Timetwister into its owner's graveyard.)

Whenever a creature enters the battlefield under your control, draw a card if its power is 3 or greater. Otherwise, put two +1/+1 counters on it.

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)

I -- Urza's Saga gains "{T}: Add {C}."

II -- Urza's Saga gains "{2}, {T}: Create a 0/0 colorless Construct artifact creature token with 'This creature gets +1/+1 for each artifact you control.'"

III -- Search your library for an artifact card with mana cost {0} or {1}, put it onto the battlefield, then shuffle.

Flash

Other Merfolk you control get +1/+1.

Sacrifice a Merfolk: Counter target noncreature spell unless its controller pays {1}.

{T}: Add {U}. Spend this mana only to cast an instant or sorcery spell or a kicked spell.

Each player discards their hand, then draws cards equal to the greatest number of cards a player discarded this way.

Search your library for a creature card, reveal it, then shuffle and put the card on top.

Each land is a Forest in addition to its other land types.

When Zegana, Utopian Speaker enters the battlefield, 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.