Preordain

Scry 2, then draw a card. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Island

Merrow Reejerey

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

Catalog

Comparative Analysis

Surge {2}{U} (You may cast this spell for its surge cost if you or a teammate has cast another spell this turn.)
Target player draws two cards.

Triton Shorestalker

River Sneak

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

Path of Ancestry

Path of Ancestry enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Merrow Levitator

{T}: Target creature gains flying until end of turn.
Whenever you cast a blue spell, you may untap Merrow Levitator.

Wind Strider

Flash (You may cast this spell any time you could cast an instant.)
Flying

Vapor Snag

Return target creature to its owner's hand. Its controller loses 1 life.

Deepchannel Mentor

Blue creatures you control can't be blocked.

Stonybrook Banneret

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.

Library Larcenist

Whenever Library Larcenist attacks, draw a card.

Sandbar Merfolk

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

Compulsive Research

Target player draws three cards. Then that player discards two cards unless they discard a land card.

Aquitect's Will

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.

Tideshaper Mystic

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

Deep Analysis

Target player draws two cards.
Flashback—{1}{U}, Pay 3 life. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Crashing Tide

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

Merfolk Looter

Fleeting Distraction

Target creature gets -1/-0 until end of turn.
Draw a card.

Merfolk of the Pearl Trident

Triton Shorethief

Inkfathom Divers

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
When Inkfathom Divers enters, look at the top four cards of your library, then put them back in any order.

Distant Melody

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

Library of Leng

You have no maximum hand size.
If an effect causes you to discard a card, discard it, but you may put it on top of your library instead of into your graveyard.

Storm Sculptor

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

Unsummon

Return target creature to its owner's hand.

Brilliant Plan

Merfolk Spy

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Whenever Merfolk Spy deals combat damage to a player, that player reveals a card at random from their hand.

Thought Vessel

You have no maximum hand size.
{T}: Add {C}.

Apprentice Wizard

Soaring Seacliff

Soaring Seacliff enters tapped.
When Soaring Seacliff enters, target creature gains flying until end of turn.
{T}: Add {U}.

Frostwind Invoker

Flying
{8}: Creatures you control gain flying until end of turn.

Enclave Elite

Multikicker {1}{U} (You may pay an additional {1}{U} any number of times as you cast this spell.)
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Enclave Elite enters with a +1/+1 counter on it for each time it was kicked.

Divination

Mist-Cloaked Herald

Shaper Apprentice

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

Fathom Seer

Morph—Return two Islands you control to their owner's hand. (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Fathom Seer is turned face up, draw two cards.

Mana Leak

Counter target spell unless its controller pays {3}.

Cartouche of Knowledge

Enchant creature you control
When Cartouche of Knowledge enters, draw a card.
Enchanted creature gets +1/+1 and has flying.

Aether Spellbomb

{U}, Sacrifice Aether Spellbomb: Return target creature to its owner's hand.
{1}, Sacrifice Aether Spellbomb: Draw a card.

Halimar Depths

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

Halimar Wavewatch

Level up {2} ({2}: Put a level counter on this. Level up only as a sorcery.)
LEVEL 1-4
0/6
LEVEL 5+
6/6
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Fellwar Stone

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

Mulldrifter

Flying
When Mulldrifter enters, draw two cards.
Evoke {2}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Arcane Signet

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

Spell Pierce

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

Merrow Wavebreakers

{1}{U}, {Q}: Merrow Wavebreakers gains flying until end of turn. ({Q} is the untap symbol.)

Sea Scryer

Merfolk Raiders

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Phasing (This phases in or out before you untap during each of your untap steps. While it's phased out, it's treated as though it doesn't exist.)

Befuddle

Target creature gets -4/-0 until end of turn.
Draw a card.

Omen of the Sea

Flash (You may cast this spell any time you could cast an instant.)
When Omen of the Sea enters, scry 2, then draw a card.
{2}{U}, Sacrifice Omen of the Sea: Scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Walking Atlas

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

Caller of Gales

{1}{U}, {T}: Target creature gains flying until end of turn.

Manta Riders

{U}: Manta Riders gains flying until end of turn.

Last Thoughts

Draw a card.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

Ponder

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

Arctic Merfolk

Kicker—Return a creature you control to its owner's hand. (You may return a creature you control to its owner's hand in addition to any other costs as you cast this spell.)
If Arctic Merfolk was kicked, it enters with a +1/+1 counter on it.

Spreading Seas

Enchant land
When Spreading Seas enters, draw a card.
Enchanted land is an Island.

Alchemist's Vial

When Alchemist's Vial enters, draw a card.
{1}, {T}, Sacrifice Alchemist's Vial: Target creature can't attack or block this turn.

Skywatcher Adept

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

Syncopate

Counter target spell unless its controller pays {X}. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Gitaxian Probe

({U/P} can be paid with either {U} or 2 life.)
Look at target player's hand.
Draw a card.

Counterspell

Umara Entangler

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)

Tidal Warrior

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

Streambed Aquitects

{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.