Hullbreaker Horror

Flash
This spell can't be countered.
Whenever you cast a spell, choose up to one —
• Return target spell you don't control to its owner's hand.
• Return target nonland permanent to its owner's hand.

Part the Waterveil

Take an extra turn after this one. Exile Part the Waterveil.
Awaken 6—{6}{U}{U}{U} (If you cast this spell for {6}{U}{U}{U}, also put six +1/+1 counters on target land you control and it becomes a 0/0 Elemental creature with haste. It's still a land.)

Time Wipe

Return a creature you control to its owner's hand, then destroy all creatures.

Island

Shadow Rift

Target creature gains shadow until end of turn. (It can block or be blocked by only creatures with shadow.)
Draw a card.

Teferi's Protection

Until your next turn, your life total can't change and you gain protection from everything. All permanents you control phase out. (While they're phased out, they're treated as though they don't exist. They phase in before you untap during your untap step.)
Exile Teferi's Protection.

Temple of Enlightenment

This land enters tapped.
When this land enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
{T}: Add {W} or {U}.

Archmage Emeritus

Magecraft — Whenever you cast or copy an instant or sorcery spell, draw a card.

Mystical Tutor

Search your library for an instant or sorcery card, reveal it, then shuffle and put that card on top.

Murmuring Mystic

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

Prologue to Phyresis

Each opponent gets a poison counter.
Draw a card.

Angel's Grace

Split second (As long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abilities.)
You can't lose the game this turn and your opponents can't win the game this turn. Until end of turn, damage that would reduce your life total to less than 1 reduces it to 1 instead.

Snap

Return target creature to its owner's hand. Untap up to two lands.

Merchant Scroll

Search your library for a blue instant card, reveal that card, put it into your hand, then shuffle.

Beacon of Tomorrows

Target player takes an extra turn after this one. Shuffle Beacon of Tomorrows into its owner's library.

Disenchant

Astral Steel

Target creature gets +1/+2 until end of turn.
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Turnabout

Choose artifact, creature, or land. Tap all untapped permanents of the chosen type target player controls, or untap all tapped permanents of that type that player controls.

Shelter

Target creature you control gains protection from the color of your choice until end of turn.
Draw a card.

Absorb

Niblis of Frost

Flying
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast an instant or sorcery spell, tap target creature an opponent controls. That creature doesn't untap during its controller's next untap step.

Vesuvan Duplimancy

Whenever you cast a spell that targets only a single artifact or creature you control, create a token that's a copy of that artifact or creature, except it's not legendary.

Aetherflux Reservoir

Whenever you cast a spell, you gain 1 life for each spell you've cast this turn.
Pay 50 life: Aetherflux Reservoir deals 50 damage to any target.

Serpentine Curve

Create a 0/0 green and blue Fractal creature token. Put X +1/+1 counters on it, where X is one plus the total number of instant and sorcery cards you own in exile and in your graveyard.

Serum Snare

Return target nonland permanent to its owner's hand. If that permanent had mana value 3 or less, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Dawn Charm

Choose one —
• Prevent all combat damage that would be dealt this turn.
• Regenerate target creature.
• Counter target spell that targets you.

Plains

Gonti's Aether Heart

Whenever Gonti's Aether Heart or another artifact you control enters, you get {E}{E} (two energy counters).
Pay eight {E}, Exile Gonti's Aether Heart: Take an extra turn after this one.

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Azorius Signet

Ethereal Haze

Prevent all damage that would be dealt by creatures this turn.

Narset's Reversal

Copy target instant or sorcery spell, then return it to its owner's hand. You may choose new targets for the copy.

Idyllic Beachfront

({T}: Add {W} or {U}.)
Idyllic Beachfront enters tapped.

Port Town

As Port Town enters, you may reveal a Plains or Island card from your hand. If you don't, Port Town enters tapped.
{T}: Add {W} or {U}.

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

High Tide

Until end of turn, whenever a player taps an Island for mana, that player adds an additional {U}.

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Indestructible Aura

Prevent all damage that would be dealt to target creature this turn.

Elminster

Whenever you scry, the next instant or sorcery spell you cast this turn costs {X} less to cast, where X is the number of cards looked at while scrying this way.
+2: Draw a card, then scry 2.
−3: Exile the top card of your library. Create a number of 1/1 blue Faerie Dragon creature tokens with flying equal to that card's mana value.
Elminster can be your commander.

Show of Confidence

When you cast this spell, copy it for each other instant and sorcery spell you've cast this turn. You may choose new targets for the copies.
Put a +1/+1 counter on target creature. It gains vigilance until end of turn.

Solve the Equation

Search your library for an instant or sorcery card, reveal it, put it into your hand, then shuffle.

Twiddle

You may tap or untap target artifact, creature, or land.

Talrand, Sky Summoner

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

Leonin Lightscribe

Magecraft — Whenever you cast or copy an instant or sorcery spell, creatures you control get +1/+1 until end of turn.

Maze of Ith

{T}: Untap target attacking creature. Prevent all combat damage that would be dealt to and dealt by that creature this turn.

Monastery Mentor

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Whenever you cast a noncreature spell, create a 1/1 white Monk creature token with prowess.

Command Tower

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

Thought Vessel

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

Energy Arc

Untap any number of target creatures. Prevent all combat damage that would be dealt to and dealt by those creatures this turn.

Sol Ring

Prairie Stream

({T}: Add {W} or {U}.)
Prairie Stream enters tapped unless you control two or more basic lands.

Mindsplice Apparatus

Flash
At the beginning of your upkeep, put an oil counter on Mindsplice Apparatus.
Instant and sorcery spells you cast cost {1} less to cast for each oil counter on Mindsplice Apparatus.

Brain Freeze

Target player mills three cards.
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

Skycloud Expanse

Unwind

Counter target noncreature spell. Untap up to three lands.

Sentinel Tower

Whenever an instant or sorcery spell is cast during your turn, Sentinel Tower deals damage to any target equal to 1 plus the number of instant and sorcery spells cast before that spell this turn.

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Mercurial Spelldancer

Mercurial Spelldancer can't be blocked.
Whenever you cast a noncreature spell, put an oil counter on Mercurial Spelldancer.
Whenever Mercurial Spelldancer deals combat damage to a player, you may remove two oil counters from it. If you do, when you next cast an instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy.

Sanctum of Eternity

{T}: Add {C}.
{2}, {T}: Return target commander you own from the battlefield to your hand. Activate only during your turn.

Karn's Temporal Sundering

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Target player takes an extra turn after this one. Return up to one target nonland permanent to its owner's hand. Exile Karn's Temporal Sundering.

Candlekeep Inspiration

Until end of turn, creatures you control have base power and toughness X/X, where X is the number of cards you own in exile and in your graveyard that are instant cards, are sorcery cards, and/or have an Adventure.

Rewind

Counter target spell. Untap up to four lands.

Loran's Escape

Target artifact or creature gains hexproof and indestructible until end of turn. Scry 1.

Mystic Sanctuary

({T}: Add {U}.)
Mystic Sanctuary enters tapped unless you control three or more other Islands.
When Mystic Sanctuary enters untapped, you may put target instant or sorcery card from your graveyard on top of your library.

Frantic Search

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

Vega, the Watcher

Flying
Whenever you cast a spell from anywhere other than your hand, draw a card.

Deekah, Fractal Theorist

Magecraft — Whenever you cast or copy an instant or sorcery spell, create a 0/0 green and blue Fractal creature token. Put X +1/+1 counters on it, where X is that spell's mana value.
{3}{U}: Target creature token can't be blocked this turn.

Arcane Signet

Zethi, Arcane Blademaster

Multikicker {W/U}
When Zethi, Arcane Blademaster enters, exile up to X target instant cards from your graveyard, where X is the number of times Zethi was kicked. Put a kick counter on each of them.
Whenever Zethi attacks, copy each exiled card you own with a kick counter on it. You may cast the copies.

Faithful Mending

You gain 2 life, draw two cards, then discard two cards.
Flashback {1}{W}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Stenn, Paranoid Partisan

As Stenn, Paranoid Partisan enters, choose a card type other than creature or land.
Spells you cast of the chosen type cost {1} less to cast.
{1}{W}{U}: Exile Stenn. Return it to the battlefield under its owner's control at the beginning of the next end step.

Awe Strike

The next time target creature would deal damage this turn, prevent that damage. You gain life equal to the damage prevented this way.

Slip Out the Back

Put a +1/+1 counter on target creature. It phases out. (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

Reliquary Tower

You Come to a River

Choose one —
• Fight the Current — Return target nonland permanent to its owner's hand.
• Find a Crossing — Target creature gets +1/+0 until end of turn and can't be blocked this turn.

Thought Scour

Target player mills two cards.
Draw a card.

Boon of Safety

Put a shield counter on target creature. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)
Scry 1.