Venture Deeper

Target player mills four cards. (Then exile this card. You may cast the creature later from exile.)

Merfolk Secretkeeper

Merfolk Secretkeeper // Venture Deeper

Island

Mind Spring

Spell Snuff

Counter target spell.
Fateful hour — If you have 5 or less life, draw a card.

Sol Ring

Callaphe, Beloved of the Sea

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."

Wonder

Flying
As long as Wonder is in your graveyard and you control an Island, creatures you control have flying.

Ichthyomorphosis

Enchant creature
Enchanted creature loses all abilities and is a blue Fish with base power and toughness 0/1.

Propaganda

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

Sift

Stern Dismissal

Return target creature or enchantment an opponent controls to its owner's hand.

Gadwick, the Wizened

When Gadwick, the Wizened enters, draw X cards.
Whenever you cast a blue spell, tap target nonland permanent an opponent controls.

No Escape

Counter target creature or planeswalker spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.
Scry 1.

Mizzium Meddler

Flash (You may cast this spell any time you could cast an instant.)
When Mizzium Meddler enters, you may change a target of target spell or ability to Mizzium Meddler.

Psychic Corrosion

Whenever you draw a card, each opponent mills two cards.

Counterspell

Contentious Plan

Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Draw a card.

Siren Stormtamer

Flying
{U}, Sacrifice Siren Stormtamer: Counter target spell or ability that targets you or a creature you control.

Scroll Rack

{1}, {T}: Exile any number of cards from your hand face down. Put that many cards from the top of your library into your hand. Then look at the exiled cards and put them on top of your library in any order.

Thought Vessel

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

Cerulean Drake

Flying
Protection from red (This creature can't be blocked, targeted, dealt damage, enchanted, or equipped by anything red.)
Sacrifice Cerulean Drake: Counter target spell that targets you.

The Magic Mirror

This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
You have no maximum hand size.
At the beginning of your upkeep, put a knowledge counter on The Magic Mirror, then draw a card for each knowledge counter on The Magic Mirror.

Kasmina, Enigmatic Mentor

Spells your opponents cast that target a creature or planeswalker you control cost {2} more to cast.
−2: Create a 2/2 blue Wizard creature token. Draw a card, then discard a card.

Faerie Vandal

Flash (You may cast this spell any time you could cast an instant.)
Flying
Whenever you draw your second card each turn, put a +1/+1 counter on Faerie Vandal.

Deep Freeze

Enchant creature
Enchanted creature has base power and toughness 0/4, has defender, loses all other abilities, and is a blue Wall in addition to its other colors and types.

Nadir Kraken

Whenever you draw a card, you may pay {1}. If you do, put a +1/+1 counter on Nadir Kraken and create a 1/1 blue Tentacle creature token.

Overwhelmed Apprentice

When Overwhelmed Apprentice enters, each opponent mills two cards. Then you 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.)

Cancel

Naiad of Hidden Coves

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

Shadowspear

Equipped creature gets +1/+1 and has trample and lifelink.
{1}: Permanents your opponents control lose hexproof and indestructible until end of turn.
Equip {2}

Flux Channeler

Whenever you cast a noncreature spell, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Kasmina's Transmutation

Enchant creature
Enchanted creature loses all abilities and has base power and toughness 1/1.

Didn't Say Please

Counter target spell. Its controller mills three cards.

Rayne, Academy Chancellor

Whenever you or a permanent you control becomes the target of a spell or ability an opponent controls, you may draw a card. You may draw an additional card if Rayne, Academy Chancellor is enchanted.

Keep Safe

Counter target spell that targets a permanent you control.
Draw a card.

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.

Ratchet Bomb

{T}: Put a charge counter on Ratchet Bomb.
{T}, Sacrifice Ratchet Bomb: Destroy each nonland permanent with mana value equal to the number of charge counters on Ratchet Bomb.

Leyline of Anticipation

If Leyline of Anticipation is in your opening hand, you may begin the game with it on the battlefield.
You may cast spells as though they had flash.

Chasm Skulker

Whenever you draw a card, put a +1/+1 counter on Chasm Skulker.
When Chasm Skulker dies, create X 1/1 blue Squid creature tokens with islandwalk, where X is the number of +1/+1 counters on Chasm Skulker. (They can't be blocked as long as defending player controls an Island.)

Mystical Dispute

This spell costs {2} less to cast if it targets a blue spell.
Counter target spell unless its controller pays {3}.

Drowned Secrets

Whenever you cast a blue spell, target player mills two cards.

Tome Raider

Flying
When Tome Raider enters, draw a card.

Mask of Memory

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.)

Mesmeric Glare

Counter target spell with mana value 3 or less. (Then exile this card. You may cast the creature later from exile.)

Hypnotic Sprite

Hypnotic Sprite // Mesmeric Glare

Sinister Sabotage

Counter target spell.
Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Inevitable Betrayal

Suspend 3—{1}{U}{U} (Rather than cast this card from your hand, pay {1}{U}{U} and exile it with three time counters on it. At the beginning of your upkeep, remove a time counter. When the last is removed, you may cast it without paying its mana cost.)
Search target opponent's library for a creature card and put that card onto the battlefield under your control. Then that player shuffles.

Exclude

Counter target creature spell.
Draw a card.

Merfolk Looter

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.)

Frogify

Enchant creature
Enchanted creature loses all abilities and is a blue Frog creature with base power and toughness 1/1. (It loses all other card types and creature types.)

Sleep

Tap all creatures target player controls. Those creatures don't untap during that player's next untap step.

Reliquary Tower

Jace, Wielder of Mysteries

If you would draw a card while your library has no cards in it, you win the game instead.
+1: Target player mills two cards. Draw a card.
−8: Draw seven cards. Then if your library has no cards in it, you win the game.

Wavebreak Hippocamp

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

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control.)
Equip {1}

Mistcaller

Sacrifice Mistcaller: Until end of turn, if a nontoken creature would enter and it wasn't cast, exile it instead.

Oneirophage

Flying
Whenever you draw a card, put a +1/+1 counter on Oneirophage.

Murmuring Mystic

Whenever you cast an instant or sorcery spell, create a 1/1 blue Bird Illusion creature token with flying.

Frantic Search

Draw two cards, then discard two cards. Untap up to three lands.

Tempest Djinn

Flying
Tempest Djinn gets +1/+0 for each basic Island you control.

Teferi, Mage of Zhalfir

Flash
Creature cards you own that aren't on the battlefield have flash.
Each opponent can cast spells only any time they could cast a sorcery.

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 Brineborn Cutthroat.