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

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.

Blue creature spells you cast cost {1} less to cast. Whenever you cast a creature spell, target creature an opponent controls doesn't untap during its controller's next untap step.

Blue spells you cast cost {1} less to cast.

Sky Diamond enters the battlefield tapped. {T}: Add {U}.

Callaphe's power is equal to your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.) Creatures and enchantments you control have "Spells your opponents cast that target this permanent cost {1} more to cast."

Level up {1} ({1}: Put a level counter on this. Level up only as a sorcery.) LEVEL 2-3 3/3 Flying LEVEL 4+ 4/4 Flying Other Merfolk creatures you control get +1/+1.

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

Blue creatures you control can't be blocked.

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.

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.

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.

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.

Level up {U} ({U}: Put a level counter on this. Level up only as a sorcery.) LEVEL 4-6 2/4 LEVEL 7+ 3/5 At the beginning of each end step, if it's not your turn, take an extra turn after this one.

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

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

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

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

Mist-Cloaked Herald can't be blocked.

Islandwalk (This creature can't be blocked as long as defending player controls an Island.) {1}, {T}: Tap target land.

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

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

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

{3}, {T}: Search your library for a Merfolk permanent card, put it onto the battlefield, then shuffle.

{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.

When Tempest Caller enters the battlefield, 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.

Indestructible As long as your devotion to blue is less than five, Thassa isn't a creature. At the beginning of your end step, exile up to one other target creature you control, then return that card to the battlefield under your control. {3}{U}: Tap another 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.

{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.

Triton Shorestalker can't be blocked.

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

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.)

As Kindred Discovery enters the battlefield, choose a creature type. Whenever a creature you control of the chosen type enters the battlefield or attacks, draw a card.

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

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}.

You may cast spells from your hand without paying their mana costs.

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}.

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

Counter target spell.

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.")

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

Counter target instant or sorcery spell. Transmute {1}{U}{U} ({1}{U}{U}, Discard this card: Search your library for a card with the same mana value as this card, reveal it, put it into your hand, then shuffle. Transmute only as a sorcery.)

Counter target noncreature spell.

Scry 1. Draw a card.

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

Counter target spell. Untap up to four lands.

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.)

This spell can't be copied. Choose one. If an opponent has eight or more cards in their graveyard, you may choose both. • Copy target spell. You may choose new targets for the copy. (A copy of a permanent spell becomes a token.) • Create a token that's a copy of target creature.

Return target creature to its owner's hand. Untap up to two lands.

Castle Vantress enters the battlefield tapped unless you control an Island. {T}: Add {U}. {2}{U}{U}, {T}: Scry 2.

Coral Atoll enters the battlefield tapped. When Coral Atoll enters the battlefield, sacrifice it unless you return an untapped Island you control to its owner's hand. {T}: Add {C}{U}.

Desert of the Mindful enters the battlefield tapped. {T}: Add {U}. Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)

Halimar Depths enters the battlefield tapped. When Halimar Depths enters the battlefield, look at the top three cards of your library, then put them back in any order. {T}: Add {U}.

({T}: Add {U}.)

Lonely Sandbar enters the battlefield tapped. {T}: Add {U}. Cycling {U} ({U}, Discard this card: Draw a card.)

Magosi, the Waterveil enters the battlefield tapped. {T}: Add {U}. {U}, {T}: Put an eon counter on Magosi, the Waterveil. Skip your next turn. {T}, Remove an eon counter from Magosi, the Waterveil and return it to its owner's hand: Take an extra turn after this one.

({T}: Add {U}.) Mystic Sanctuary enters the battlefield tapped unless you control three or more other Islands. When Mystic Sanctuary enters the battlefield untapped, you may put target instant or sorcery card from your graveyard on top of your library.

Choose a creature type. Draw a card for each permanent you control of that type.

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

Kicker {5} (You may pay an additional {5} as you cast this spell.) Create a token that's a copy of target creature. If this spell was kicked, create five of those tokens instead.

Take an extra turn after this one.

Flying

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

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