March of Swirling Mist

As an additional cost to cast this spell, you may exile any number of blue cards from your hand. This spell costs {2} less to cast for each card exiled this way.
Up to X target creatures phase out. (While they're phased out, they're treated as though they don't exist. Each one phases in before its controller untaps during their next untap step.)

As long as X is in X's owner's opponent's hand, X's owner may cast X and activate X's abilities. That opponent can't cast X and plays with their hand revealed.
{U}{B}, {T}: Put X into target opponent's hand.
{3}{U}{B}: You may play a land or cast a spell from the hand X is in. If you cast a spell this way, you cast it without paying its mana cost.

Stolen by the Fae

Return target creature with mana value X to its owner's hand. You create X 1/1 blue Faerie creature tokens with flying.

Beacon of Unrest

Put target artifact or creature card from a graveyard onto the battlefield under your control. Shuffle Beacon of Unrest into its owner's library.

Syncopate

Counter target spell unless its controller pays {X}. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Silver Scrutiny

You may cast Silver Scrutiny as though it had flash if X is 3 or less.
Draw X cards.

Mass Manipulation

Gain control of X target creatures and/or planeswalkers.

Killing Wave

For each creature, its controller sacrifices it unless they pay X life.

Swamp

Hangarback Walker

Hangarback Walker enters the battlefield with X +1/+1 counters on it.
When Hangarback Walker dies, create a 1/1 colorless Thopter artifact creature token with flying for each +1/+1 counter on Hangarback Walker.
{1}, {T}: Put a +1/+1 counter on Hangarback Walker.

Finale of Eternity

Destroy up to three target creatures with toughness X or less. If X is 10 or more, return all creature cards from your graveyard to the battlefield.

Persuasion

Enchant creature (Target a creature as you cast this. This card enters the battlefield attached to that creature.)
You control enchanted creature.

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.

Endless One

Endless One enters the battlefield with X +1/+1 counters on it.

Xander's Pact

Casualty 2 (As you cast this spell, you may sacrifice a creature with power 2 or greater. When you do, copy this spell.)
Each opponent exiles the top card of their library. You may cast spells from among those cards this turn. If you cast a spell this way, pay life equal to that spell's mana value rather than pay its mana cost.

Head Games

Target opponent puts the cards from their hand on top of their library. Search that player's library for that many cards. The player puts those cards into their hand, then shuffles.

Plagiarize

Until end of turn, if target player would draw a card, instead that player skips that draw and you draw a card.

Change of Plans

Each of X target creatures you control connive. You may have any number of them phase out. (To have a creature connive, draw a card, then discard a card. If you discarded a nonland card, put a +1/+1 counter on that creature. Treat phased-out permanents and anything attached to them as though they don't exist until their controller's next turn.)

Doomed Necromancer

{B}, {T}, Sacrifice Doomed Necromancer: Return target creature card from your graveyard to the battlefield.

Royal Assassin

Xathrid Demon

Flying, trample
At the beginning of your upkeep, sacrifice a creature other than Xathrid Demon, then each opponent loses life equal to the sacrificed creature's power. If you can't sacrifice a creature, tap Xathrid Demon and you lose 7 life.

Stonecoil Serpent

Reach, trample, protection from multicolored
Stonecoil Serpent enters the battlefield with X +1/+1 counters on it.

Ugin's Conjurant

Ugin's Conjurant enters the battlefield with X +1/+1 counters on it.
If damage would be dealt to Ugin's Conjurant while it has a +1/+1 counter on it, prevent that damage and remove that many +1/+1 counters from Ugin's Conjurant.

Blue Sun's Twilight

Gain control of target creature with mana value X or less. If X is 5 or more, create a token that's a copy of that creature.

Rain of Tears

Telepathy

Your opponents play with their hands revealed.

Quicksand

{T}: Add {C}.
{T}, Sacrifice Quicksand: Target attacking creature without flying gets -1/-2 until end of turn.

Disrupting Shoal

You may exile a blue card with mana value X from your hand rather than pay this spell's mana cost.
Counter target spell if its mana value is X.

Robe of Mirrors

Enchant creature (Target a creature as you cast this. This card enters the battlefield attached to that creature.)
Enchanted creature has shroud. (It can't be the target of spells or abilities.)

Nekrataal

First strike
When Nekrataal enters the battlefield, destroy target nonartifact, nonblack creature. That creature can't be regenerated.

Loxodon Warhammer

Equipped creature gets +3/+0 and has trample and lifelink.
Equip {3}

Condescend

Counter target spell unless its controller pays {X}. 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.)

Multiple Choice

If X is 1, scry 1, then draw a card.
If X is 2, you may choose a player. They return a creature they control to its owner's hand.
If X is 3, create a 4/4 blue and red Elemental creature token.
If X is 4 or more, do all of the above.

Sphere of Annihilation

Sphere of Annihilation enters the battlefield with X void counters on it.
At the beginning of your upkeep, exile Sphere of Annihilation, all creatures and planeswalkers with mana value less than or equal to the number of void counters on it, and all creature and planeswalker cards in graveyards with mana value less than or equal to the number of void counters on it.

Commander's Insight

Target player draws X cards plus an additional card for each time they've cast a commander from the command zone this game.

Pull from Tomorrow

Terramorphic Expanse

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

Diabolic Tutor

Search your library for a card, put that card into your hand, then shuffle.

Underworld Dreams

Whenever an opponent draws a card, Underworld Dreams deals 1 damage to that player.

Entrancing Melody

Gain control of target creature with mana value X.

Arcanis the Omnipotent

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

Merfolk Looter

Mortivore

Mortivore's power and toughness are each equal to the number of creature cards in all graveyards.
{B}: Regenerate Mortivore.

Island

Gadwick, the Wizened

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

Peek

Look at target player's hand.
Draw a card.

Gravedigger

When Gravedigger enters the battlefield, you may return target creature card from your graveyard to your hand.

Clone

You may have Clone enter the battlefield as a copy of any creature on the battlefield.

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}.

Xathrid Slyblade

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
{3}{B}: Until end of turn, Xathrid Slyblade loses hexproof and gains first strike and deathtouch. (It deals combat damage before creatures without first strike. Any amount of damage it deals to a creature is enough to destroy it.)

Icy Manipulator

{1}, {T}: Tap target artifact, creature, or land.

Profane Command

Choose two —
• Target player loses X life.
• Return target creature card with mana value X or less from your graveyard to the battlefield.
• Target creature gets -X/-X until end of turn.
• Up to X target creatures gain fear until end of turn. (They can't be blocked except by artifact creatures and/or black creatures.)

Curse of the Swine

Exile X target creatures. For each creature exiled this way, its controller creates a 2/2 green Boar creature token.

Mind Stone

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

Mind Spring

Extract Brain

Target opponent chooses X cards from their hand. Look at those cards. You may cast a spell from among them without paying its mana cost.

Terror

Destroy target nonartifact, nonblack creature. It can't be regenerated.

Xanathar, Guild Kingpin

At the beginning of your upkeep, choose target opponent. Until end of turn, that player can't cast spells, you may look at the top card of their library any time, you may play the top card of their library, and you may spend mana as though it were mana of any color to cast spells this way.

Phyrexian Rager

When Phyrexian Rager enters the battlefield, you draw a card and you lose 1 life.

Sculpting Steel

You may have Sculpting Steel enter the battlefield as a copy of any artifact on the battlefield.

Ingenious Mastery

You may pay {2}{U} rather than pay this spell's mana cost.
If the {2}{U} cost was paid, you draw three cards, then an opponent creates two Treasure tokens and they scry 2. If that cost wasn't paid, you draw X cards.

Cancel

Hypnotic Specter

Flying
Whenever Hypnotic Specter deals damage to an opponent, that player discards a card at random.

Assassinate

Xathrid Gorgon

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
{2}{B}, {T}: Put a petrification counter on target creature. It gains defender and becomes a colorless artifact in addition to its other types. Its activated abilities can't be activated. (A creature with defender can't attack.)