Borrowing 100,000 Arrows

Draw a card for each tapped creature target opponent controls.

Coastal Breach

Undaunted (This spell costs {1} less to cast for each opponent.)
Return all nonland permanents to their owners' hands.

Talrand, Sky Summoner

Whenever you cast an instant or sorcery spell, create a 2/2 blue Drake creature token with flying.

Wavebreak Hippocamp

Whenever you cast your first spell during each opponent's turn, draw a card.

Counterspell

Arcanis the Omnipotent

{T}: Draw three cards.
{2}{U}{U}: Return Arcanis the Omnipotent to its owner's hand.

Omenspeaker

When Omenspeaker enters the battlefield, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Shipbreaker Kraken

{6}{U}{U}: Monstrosity 4. (If this creature isn't monstrous, put four +1/+1 counters on it and it becomes monstrous.)
When Shipbreaker Kraken becomes monstrous, tap up to four target creatures. Those creatures don't untap during their controllers' untap steps for as long as you control Shipbreaker Kraken.

Telling Time

Look at the top three cards of your library. Put one of those cards into your hand, one on top of your library, and one on the bottom of your library.

Master of Waves

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.)

Perilous Voyage

Return target nonland permanent you don't control to its owner's hand. If its mana value was 2 or less, scry 2.

Academy Journeymage

This spell costs {1} less to cast if you control a Wizard.
When Academy Journeymage enters the battlefield, return target creature an opponent controls to its owner's hand.

Depths of Desire

Return target creature to its owner's hand. Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Reliquary Tower

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

Svyelun of Sea and Sky

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}.)

Coastal Drake

Flying
{1}{U}, {T}: Return target Kavu to its owner's hand.

Lone Revenant

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Whenever Lone Revenant deals combat damage to a player, if you control no other creatures, look at the top four cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.

Tidebinder Mage

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.

Merfolk Mesmerist

Terramorphic Expanse

{T}, Sacrifice Terramorphic Expanse: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Sage of Fables

Each other Wizard creature you control enters the battlefield with an additional +1/+1 counter on it.
{2}, Remove a +1/+1 counter from a creature you control: Draw a card.

Evolving Wilds

{T}, Sacrifice Evolving Wilds: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Cosi's Trickster

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

Levitation

Vortex Elemental

{U}: Put Vortex Elemental and each creature blocking or blocked by it on top of their owners' libraries, then those players shuffle.
{3}{U}{U}: Target creature blocks Vortex Elemental this turn if able.

Sight Beyond Sight

Look at the top two cards of your library. Put one of them into your hand and the other on the bottom of your library.
Rebound (If you cast this spell from your hand, exile it as it resolves. At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.)

Pieces of the Puzzle

Reveal the top five cards of your library. Put up to two instant and/or sorcery cards from among them into your hand and the rest into your graveyard.

Voyage's End

Return target creature to its owner's hand. Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Trail of Evidence

Whenever you cast an instant or sorcery spell, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Merfolk Sovereign

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

Defy Gravity

Target creature gains flying until end of turn.
Flashback {U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Anticipate

Look at the top three cards of your library. Put one of them into your hand and the rest on the bottom of your library in any order.

Trade Routes

{1}: Return target land you control to its owner's hand.
{1}, Discard a land card: Draw a card.

Silumgar Spell-Eater

Megamorph {4}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its megamorph cost and put a +1/+1 counter on it.)
When Silumgar Spell-Eater is turned face up, counter target spell unless its controller pays {3}.

Lullmage Mentor

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.

Umara Entangler

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

Shaper Apprentice

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

Into the Void

Return up to two target creatures to their owners' hands.

Dakra Mystic

{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.

Kraken Hatchling

Oblivion Sower

When you cast this spell, target opponent exiles the top four cards of their library, then you may put any number of land cards that player owns from exile onto the battlefield under your control.

Kopala, Warden of Waves

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.

Homarid Explorer

When Homarid Explorer enters the battlefield, target player mills four cards.

Coastal Discovery

Draw two cards.
Awaken 4—{5}{U} (If you cast this spell for {5}{U}, also put four +1/+1 counters on target land you control and it becomes a 0/0 Elemental creature with haste. It's still a land.)

Wizard's Retort

This spell costs {1} less to cast if you control a Wizard.
Counter target spell.

Stormtide Leviathan

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.

Vodalian Arcanist

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

Reckless Scholar

{T}: Target player draws a card, then discards a card.

Cloudreader Sphinx

Flying
When Cloudreader Sphinx enters the battlefield, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Passwall Adept

{2}{U}: Target creature can't be blocked this turn.

Thassa's Ire

{3}{U}: You may tap or untap target creature.

Sigiled Starfish

{T}: Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Ominous Seas

Whenever you draw a card, put a foreshadow counter on Ominous Seas.
Remove eight foreshadow counters from Ominous Seas: Create an 8/8 blue Kraken creature token.
Cycling {2} ({2}, Discard this card: Draw a card.)

Tide Shaper

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.

Willbender

Morph {1}{U} (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 Willbender is turned face up, change the target of target spell or ability with a single target.

Archaeomancer

When Archaeomancer enters the battlefield, return target instant or sorcery card from your graveyard to your hand.

Riverwise Augur

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

Nephalia Moondrakes

Flying
When Nephalia Moondrakes enters the battlefield, target creature gains flying until end of turn.
{4}{U}{U}, Exile Nephalia Moondrakes from your graveyard: Creatures you control gain flying until end of turn.

Clutch of Currents

Return target creature to its owner's hand.
Awaken 3—{4}{U} (If you cast this spell for {4}{U}, also put three +1/+1 counters on target land you control and it becomes a 0/0 Elemental creature with haste. It's still a land.)

Coastal Piracy

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

Coastal Wizard

{T}: Return Coastal Wizard and another target creature to their owners' hands. Activate only during your turn, before attackers are declared.

Coastal Hornclaw

Sacrifice a land: Coastal Hornclaw gains flying until end of turn.

Island

Silvergill Adept

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.

Magus of the Unseen

{1}{U}, {T}: Untap target artifact an opponent controls and gain control of it until end of turn. It gains haste until end of turn. When you lose control of the artifact, tap it.

Harbinger of the Tides

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.

Windrider Patrol

Flying
Whenever Windrider Patrol deals combat damage to a player, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Crystalline Nautilus

Bestow {3}{U}{U} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)
When Crystalline Nautilus becomes the target of a spell or ability, sacrifice it.
Enchanted creature gets +4/+4 and has "When this creature becomes the target of a spell or ability, sacrifice it."

Harbor Serpent

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Harbor Serpent can't attack unless there are five or more Islands on the battlefield.

Exultant Cultist

Wave-Wing Elemental

Flying
Landfall — Whenever a land enters the battlefield under your control, Wave-Wing Elemental gets +2/+2 until end of turn.