Have

Serpentine Ambush

Until end of turn, target creature becomes a blue Serpent with base power and toughness 5/5.

Distortion Strike

Target creature gets +1/+0 until end of turn and can't be blocked this turn.
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.)

Secrets of the Key

Investigate. If this spell was cast from a graveyard, investigate twice instead. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")
Flashback {3}{U}

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

Remote Isle

This land enters tapped.
{T}: Add {U}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Nephalia Seakite

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

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Shaper Apprentice

This creature has flying as long as you control another Merfolk.

Prismatic Lens

{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Psionic Snoop

Flash
When this creature enters, it connives. (Draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on this creature.)

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.

Arcane Signet

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

Refute

Counter target spell. Draw a card, then discard a card.

Riptide Turtle

Skyline Cascade

This land enters tapped.
When this land enters, target creature an opponent controls doesn't untap during its controller's next untap step.
{T}: Add {U}.

Study Hall

{T}: Add {C}.
{1}, {T}: Add one mana of any color. When you spend this mana to cast your commander, scry X, where X is the number of times it's been cast from the command zone this game.

Cliffhaven Kitesail

When this Equipment enters, attach it to target creature you control.
Equipped creature has flying.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Thought Vessel

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

Chrome Prowler

Flash
When this creature enters, tap target creature an opponent controls.

Nivix Barrier

Flash (You may cast this spell any time you could cast an instant.)
Defender (This creature can't attack.)
When this creature enters, target attacking creature gets -4/-0 until end of turn.

Ornithopter of Paradise

Arcane Denial

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.

Cloak of Mists

Enchant creature
Enchanted creature can't be blocked.

Scour All Possibilities

Scry 2, then draw a card.
Flashback {4}{U} (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.

Starlit Mantle

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature you control
When this Aura enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

Saiba Cryptomancer

Flash
Backup 1 (When this creature enters, put a +1/+1 counter on target creature. If that's another creature, it gains the following ability until end of turn.)
Hexproof

Desert of the Mindful

This land enters tapped.
{T}: Add {U}.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)

Aven Reedstalker

Pestermite

Flash
Flying
When this creature enters, you may tap or untap target permanent.

Ophidian Eye

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Whenever enchanted creature deals damage to an opponent, you may draw a card.

Sky Diamond

This artifact enters tapped.
{T}: Add {U}.

Brass Knuckles

When you cast this spell, copy it. (The copy becomes a token.)
Equipped creature has double strike as long as two or more Equipment are attached to it.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Soaring Seacliff

This land enters tapped.
When this land enters, target creature gains flying until end of turn.
{T}: Add {U}.

Omen of the Sea

Flash (You may cast this spell any time you could cast an instant.)
When this enchantment enters, scry 2, then draw a card.
{2}{U}, Sacrifice this enchantment: 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.)

Naiad of Hidden Coves

During turns other than yours, spells you cast cost {1} less to cast.

Island

Crystacean

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

Behold the Multiverse

Scry 2, then draw two cards.
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.)

Brineborn Cutthroat

Flash (You may cast this spell any time you could cast an instant.)
Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on this creature.

Radiant Fountain

When this land enters, you gain 2 life.
{T}: Add {C}.

Opal Palace

{T}: Add {C}.
{1}, {T}: Add one mana of any color in your commander's color identity. If you spend this mana to cast your commander, it enters with a number of additional +1/+1 counters on it equal to the number of times it's been cast from the command zone this game.

Prismwake Merrow

Flash
When this creature enters, target permanent becomes the color or colors of your choice until end of turn.

Humbling Elder

Flash
When this creature enters, target creature an opponent controls gets -2/-0 until end of turn.

Faerie Invaders

Whispersilk Cloak

Equipped creature can't be blocked and has shroud. (It can't be the target of spells or abilities.)
Equip {2}

Artful Dodge

Target creature can't be blocked this turn.
Flashback {U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Neurok Stealthsuit

Equipped creature has shroud. (It can't be the target of spells or abilities.)
{U}{U}: Attach this Equipment to target creature you control.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Faerie Duelist

Flash
Flying
When this creature enters, target creature an opponent controls gets -2/-0 until end of turn.

Mantle of Tides

Equipped creature gets +1/+2.
Whenever you draw your second card each turn, attach this Equipment to target creature you control.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

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.

Utter Insignificance

Flash
Enchant creature
Enchanted creature loses all abilities and has base power and toughness 1/1.
{2}{C}: Exile enchanted creature.

Awesome Presence

Enchant creature
Enchanted creature can't be blocked unless defending player pays {3} for each creature they control that's blocking it.

Brinebarrow Intruder

Eel Umbra

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Enchanted creature gets +1/+1.
Umbra armor (If enchanted creature would be destroyed, instead remove all damage from it and destroy this Aura.)

Zulaport Duelist

Flash
When this creature enters, up to one target creature gets -2/-0 until end of turn. Its controller mills two cards. (They put the top two cards of their library into their graveyard.)

Brainstorm

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

Dire Mimic

Flash
{T}, Sacrifice this artifact: Add one mana of any color.
{3}: This artifact becomes a Shapeshifter artifact creature with base power and toughness 5/5 until end of turn.

Forge of Heroes

{T}: Add {C}.
{T}: Choose target commander that entered this turn. Put a +1/+1 counter on it if it's a creature and a loyalty counter on it if it's a planeswalker.

Grey Havens Navigator

Lonely Sandbar

This land enters tapped.
{T}: Add {U}.
Cycling {U} ({U}, Discard this card: Draw a card.)

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.)

Sentinels of Glen Elendra

Infiltrator's Magemark

Enchant creature
Creatures you control that are enchanted get +1/+1 and can't be blocked except by creatures with defender.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice this artifact: Draw a card.

Wind Strider

Vexing Gull

Decanter of Endless Water

You have no maximum hand size.
{T}: Add one mana of any color.

Quick-Draw Dagger

Flash
When this Equipment enters, attach it to target creature you control. That creature gains first strike until end of turn.
Equipped creature gets +1/+1.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Aqueous Form

Enchant creature
Enchanted creature can't be blocked.
Whenever enchanted creature attacks, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Conduit Pylons

When this land enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Echoing Truth

Return target nonland permanent and all other permanents with the same name as that permanent to their owners' hands.

Silent Departure

Return target creature to its owner's hand.
Flashback {4}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Spellstutter Sprite

Flash
Flying
When this creature enters, counter target spell with mana value X or less, where X is the number of Faeries you control.

Clammy Prowler

Whenever this creature attacks, another target attacking creature can't be blocked this turn.

Think Twice

Draw a card.
Flashback {2}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Halimar Depths

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

Buoyancy

Flash
Enchant creature
Enchanted creature has flying.

Cave of Temptation

{T}: Add {C}.
{1}, {T}: Add one mana of any color.
{4}, {T}, Sacrifice this land: Put two +1/+1 counters on target creature. Activate only as a sorcery.

Blink of an Eye

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
Return target nonland permanent to its owner's hand. If this spell was kicked, draw a card.

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.)

Sapphire Charm

Choose one —
• Target player draws a card at the beginning of the next turn's upkeep.
• Target creature gains flying until end of turn.
• Target creature an opponent controls phases out. (While it's phased out, it's treated as though it doesn't exist. It phases in before its controller untaps during their next untap step.)

Cloaked Siren

Fellwar Stone

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

Bounce Off

Return target creature or Vehicle to its owner's hand.

Undersea Invader

Flash (You may cast this spell any time you could cast an instant.)
This creature enters tapped.

Enter the Enigma

Target creature can't be blocked this turn.
Draw a card.

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.

Dewdrop Spy

Flash
Flying
When this creature enters, look at the top card of target player's library.

Crystal Grotto

When this land enters, scry 1.
{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Cradle of Safety

Flash
Enchant creature you control
When this Aura enters, enchanted creature gains hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)
Enchanted creature gets +1/+1.

Counterspell

Scion of Stygia

Flash
Cone of Cold — When this creature enters, choose target creature an opponent controls, then roll a d20.
1—9 | Tap that creature.
10—20 | Tap that creature. It doesn't untap during its controller's next untap step.

Deduce

Draw a card. Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")