Sage of Mysteries

Constellation — Whenever an enchantment enters the battlefield under your control, target player mills two cards.

Breaching Hippocamp

Flash (You may cast this spell any time you could cast an instant.)
When Breaching Hippocamp enters the battlefield, untap another target creature you control.

Ordeal of Thassa

Enchant creature
Whenever enchanted creature attacks, put a +1/+1 counter on it. Then if it has three or more +1/+1 counters on it, sacrifice Ordeal of Thassa.
When you sacrifice Ordeal of Thassa, draw two cards.

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.

Mirrormade

You may have Mirrormade enter the battlefield as a copy of any artifact or enchantment on the battlefield.

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.

Thassa's Intervention

Choose one —
• Look at the top X cards of your library. Put up to two of them into your hand and the rest on the bottom of your library in a random order.
• Counter target spell unless its controller pays twice {X}.

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.

Thassa, Deep-Dwelling

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.

Dungeon Geists

Flying
When Dungeon Geists enters the battlefield, tap target creature an opponent controls. That creature doesn't untap during its controller's untap step for as long as you control Dungeon Geists.

Filigree Familiar

When Filigree Familiar enters the battlefield, you gain 2 life.
When Filigree Familiar dies, draw a card.

Protean Thaumaturge

Constellation — Whenever an enchantment enters the battlefield under your control, you may have Protean Thaumaturge become a copy of another target creature, except it has this ability.

Invisibility

Enchant creature
Enchanted creature can't be blocked except by Walls.

Muse Drake

Flying
When Muse Drake enters the battlefield, draw a card.

Aether Barrier

Whenever a player casts a creature spell, that player sacrifices a permanent unless they pay {1}.

Thassa's Rebuff

Counter target spell unless its controller pays {X}, where X is your devotion to blue. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Armillary Sphere

{2}, {T}, Sacrifice Armillary Sphere: Search your library for up to two basic land cards, reveal them, put them into your hand, then shuffle.

Triton Waverider

Constellation — Whenever an enchantment enters the battlefield under your control, Triton Waverider gains flying until end of turn.

Eel Umbra

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

Bident of Thassa

Whenever a creature you control deals combat damage to a player, you may draw a card.
{1}{U}, {T}: Creatures your opponents control attack this turn if able.

Barrin, Tolarian Archmage

When Barrin, Tolarian Archmage enters the battlefield, return up to one other target creature or planeswalker to its owner's hand.
At the beginning of your end step, if a permanent was put into your hand from the battlefield this turn, draw a card.

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice Mind Stone: Draw a card.

Perplexing Chimera

Whenever an opponent casts a spell, you may exchange control of Perplexing Chimera and that spell. If you do, you may choose new targets for the spell. (If the spell becomes a permanent, you control that permanent.)

Omen of the Sea

Flash
When Omen of the Sea enters the battlefield, scry 2, then draw a card.
{2}{U}, Sacrifice Omen of the Sea: Scry 2.

Starlit Mantle

Flash
Enchant creature you control
When Starlit Mantle enters the battlefield, 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.

Peregrine Drake

Flying
When Peregrine Drake enters the battlefield, untap up to five lands.

Archetype of Imagination

Creatures you control have flying.
Creatures your opponents control lose flying and can't have or gain flying.

Thassa's Devourer

Constellation — Whenever Thassa's Devourer or another enchantment enters the battlefield under your control, target player mills two cards.

Frozen Solid

Enchant creature
Enchanted creature doesn't untap during its controller's untap step.
When enchanted creature is dealt damage, destroy it.

Hypnotic Siren

Bestow {5}{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.)
Flying
You control enchanted creature.
Enchanted creature gets +1/+1 and has flying.

Thassa's Oracle

When Thassa's Oracle enters the battlefield, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Nyxborn Triton

Bestow {4}{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.)
Enchanted creature gets +2/+3.

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."

Augur of Bolas

When Augur of Bolas enters the battlefield, look at the top three cards of your library. You may reveal an instant or sorcery card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Infinite Reflection

Enchant creature
When Infinite Reflection enters the battlefield attached to a creature, each other nontoken creature you control becomes a copy of that creature.
Nontoken creatures you control enter the battlefield as a copy of enchanted creature.

Omniscience

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

Frost Lynx

When Frost Lynx enters the battlefield, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Icefall Regent

Flying
When Icefall Regent enters the battlefield, tap target creature an opponent controls. That creature doesn't untap during its controller's untap step for as long as you control Icefall Regent.
Spells your opponents cast that target Icefall Regent cost {2} more to cast.

Agent of Treachery

When Agent of Treachery enters the battlefield, gain control of target permanent.
At the beginning of your end step, if you control three or more permanents you don't own, draw three cards.

Aether Tunnel

Enchant creature
Enchanted creature gets +1/+0 and can't be blocked.

Shoal Kraken

Constellation — Whenever an enchantment enters the battlefield under your control, you may draw a card. If you do, discard a card.

Sower of Temptation

Flying
When Sower of Temptation enters the battlefield, gain control of target creature for as long as Sower of Temptation remains on the battlefield.

Cavalier of Gales

Flying
When Cavalier of Gales enters the battlefield, draw three cards, then put two cards from your hand on top of your library in any order.
When Cavalier of Gales dies, shuffle it into its owner's library, then scry 2.

Portal of Sanctuary

{1}, {T}: Return target creature you control and each Aura attached to it to their owners' hands. Activate only during your turn.

Wavebreak Hippocamp

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

Serpent of Yawning Depths

Krakens, Leviathans, Octopuses, and Serpents you control can't be blocked except by Krakens, Leviathans, Octopuses, and Serpents.

Counterspell

Cancel

Augury Owl

Flying
When Augury Owl enters the battlefield, scry 3. (Look at the top three cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Aethersnipe

When Aethersnipe enters the battlefield, return target nonland permanent to its owner's hand.
Evoke {1}{U}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters the battlefield.)

Scholar of Stars

When Scholar of Stars enters the battlefield, if you control an artifact, draw a card.

Witness of Tomorrows

Thassa's Ire

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

Cloudkin Seer

Flying
When Cloudkin Seer enters the battlefield, draw a card.

Air Bladder

Enchant creature
Enchanted creature has flying.
Enchanted creature can block only creatures with flying.

Whitewater Naiads

Constellation — Whenever Whitewater Naiads or another enchantment enters the battlefield under your control, target creature can't be blocked this turn.

Angler Drake

Flying
When Angler Drake enters the battlefield, you may return target creature to its owner's hand.

Arcane Flight

Enchant creature
Enchanted creature gets +1/+1 and has flying.

Curse of Verbosity

Enchant player
Whenever enchanted player is attacked, you draw a card. Each opponent attacking that player does the same.

Aether Adept

When Aether Adept enters the battlefield, return target creature to its owner's hand.

Thassa's Emissary

Bestow {5}{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.)
Whenever Thassa's Emissary or enchanted creature deals combat damage to a player, draw a card.
Enchanted creature gets +3/+3.

Eidolon of Philosophy

{6}{U}, Sacrifice Eidolon of Philosophy: Draw three cards.

Flight

Enchant creature
Enchanted creature has flying.

Nyxborn Seaguard

Precursor Golem

When Precursor Golem enters the battlefield, create two 3/3 colorless Golem artifact creature tokens.
Whenever a player casts an instant or sorcery spell that targets only a single Golem, that player copies that spell for each other Golem that spell could target. Each copy targets a different one of those Golems.

Riptide Chimera

Flying
At the beginning of your upkeep, return an enchantment you control to its owner's hand.