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.

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.

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

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

Whenever a creature you control deals combat damage to an opponent, you may draw a card.

Whenever an opponent shuffles their library, you may put a +1/+1 counter on Cosi's Trickster.

Counter target spell.

Choose any number of creatures target player controls. Choose the same number of creatures another target player controls. Those players exchange control of those creatures. (This effect lasts indefinitely.)

{U}, {T}: Each player reveals the top card of their library. You may put the revealed cards into their owners' graveyards. If you don't, each player draws a card.

Return to their owners' hands all creatures with toughness less than or equal to the number of Islands you control.

{T}: Add one mana of any color that a land an opponent controls could produce.

Draw a card for each Island you control.

Enchant creature, land, or planeswalker

Enchanted permanent is a colorless land with "{T}: Add {C}" and loses all other card types and abilities.

({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}.)

({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}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

({T}: Add {U}.)

At the beginning of each player's draw step, that player draws an additional card.

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.

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

Equip {0}

{T}: Add {C}.

{T}: Target nonland permanent becomes an artifact in addition to its other types until end of turn.

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 unless its controller pays {3}.

Whenever equipped creature deals combat damage to a player, you may draw two cards. If you do, discard a card.

Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Protection from red

Elemental creatures you control get +1/+1.

When Master of Waves enters the battlefield, 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.)

{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.

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

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

When Merrow Harbinger enters the battlefield, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.

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

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

{T}: Add {C}.

{2}, {T}: Each player draws a card.

{T}: Add {C}.

{1}, {T}, Sacrifice Mind Stone: Draw a card.

{1}, {T}, Sacrifice Moonsilver Key: Search your library for an artifact card with a mana ability or a basic land card, reveal it, put it into your hand, then shuffle.

Choose target nonlegendary creature. The next time one or more creatures or planeswalkers enter the battlefield this turn, they enter as copies of the chosen creature.

Foretell {U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Counter target noncreature spell.

Scry 1.

Draw a card.

{3}{U}, {T}, Discard a card: Untap target creature and gain control of it until end of turn. That creature gains haste until end of turn.

Look at the top three cards of your library, then put them back in any order. You may shuffle.

Draw a card.

Destroy target creature. It can't be regenerated. Its controller creates a 3/3 green Ape creature token.

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

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

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

Delirium -- {2}{U}, {T}: Draw a card. Activate only if there are four or more card types among cards in your graveyard.

Exile target creature. Its controller manifests the top card of their library. (That player puts the top card of their library onto the battlefield face down as a 2/2 creature. If it's a creature card, it can be turned face up any time for its mana cost.)

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

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

You have no maximum hand size.

{T}: Add {C}.

River Sneak can't be blocked.

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

Counter target spell.

Foretell {1}{U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Scry 2, then draw a card.

Flashback {4}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

When Scourge of Fleets enters the battlefield, return each creature your opponents control with toughness X or less to its owner's hand, where X is the number of Islands you control.

{T}: Add {C}.

{1}, {T}: Add {U}.

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

When you control no Islands, sacrifice Seasinger.

You may choose not to untap Seasinger during your untap step.

{T}: Gain control of target creature whose controller controls an Island for as long as you control Seasinger and Seasinger remains tapped.

Sky Diamond enters the battlefield tapped.

{T}: Add {U}.

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

Return target creature to its owner's hand.

{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.

{T}: Add {C}. Put a point counter on Strixhaven Stadium.

Whenever a creature deals combat damage to you, remove a point counter from Strixhaven Stadium.

Whenever a creature you control deals combat damage to an opponent, put a point counter on Strixhaven Stadium. Then if it has ten or more point counters on it, remove them all and that player loses the game.

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}.)

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control.)

Equip {1}

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

{T}: Add {C}.

{2}, {T}: You may put a basic land card from your hand onto the battlefield tapped.

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.

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.

You have no maximum hand size.

{T}: Add {C}.

Any player may cast spells as though they had flash.

Your opponents can't cast spells during your turn.

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

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.

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.

{T}: Target land becomes the basic land type of your choice until end of turn. Activate only during your turn.

{T}: Add {C}.

{3}, {T}, Pay life equal to the number of colors in your commanders' color identity: Draw a card.