Broken Ambitions

Counter target spell unless its controller pays {X}. Clash with an opponent. If you win, that spell's controller mills four cards. (Each clashing player reveals the top card of their library, then puts that card on the top or bottom. A player wins if their card had a higher mana value.)

Merrow Witsniper

When Merrow Witsniper enters, target player mills a card.

Stream of Thought

Target player mills four cards. You shuffle up to four cards from your graveyard into your library.
Replicate {2}{U}{U} (When you cast this spell, copy it for each time you paid its replicate cost. You may choose new targets for the copies.)

Paranoid Delusions

Target player mills three cards.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

Horrifying Revelation

Target player discards a card, then mills a card.

Griptide

Put target creature on top of its owner's library.

Jace's Erasure

Whenever you draw a card, you may have target player mill a card.

Shriekhorn

Shriekhorn enters with three charge counters on it.
{T}, Remove a charge counter from Shriekhorn: Target player mills two cards.

Drowner Initiate

Whenever a player casts a blue spell, you may pay {1}. If you do, target player mills two cards.

Dampen Thought

Target player mills four cards.
Splice onto Arcane {1}{U} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)

Brainstorm

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

Returned Reveler

When Returned Reveler dies, each player mills three cards.

Mind Sculpt

Swamp

Countermand

Counter target spell. Its controller mills four cards.

Island

Thassa's Bounty

Draw three cards. Target player mills three cards.

Psychic Strike

Counter target spell. Its controller mills two cards.

Dreadwaters

Target player mills X cards, where X is the number of lands you control.

Shriekgeist

Flying
Whenever Shriekgeist deals combat damage to a player, that player mills two cards.

Gelid Shackles

Enchant creature
Enchanted creature can't block, and its activated abilities can't be activated.
{S}: Enchanted creature gains defender until end of turn. ({S} can be paid with one mana from a snow source.)

Book Burning

Any player may have Book Burning deal 6 damage to them. If no one does, target player mills six cards.

Balustrade Spy

Flying
When Balustrade Spy enters, target player reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.

Selhoff Occultist

Whenever Selhoff Occultist or another creature dies, target player mills a card.

Compelling Argument

Target player mills five cards.
Cycling {U} ({U}, Discard this card: Draw a card.)

Thought Collapse

Counter target spell. Its controller mills three cards.

Homarid Explorer

When Homarid Explorer enters, target player mills four cards.

Dream Twist

Target player mills three cards.
Flashback {1}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Crosstown Courier

Whenever Crosstown Courier deals combat damage to a player, that player mills that many cards.

Sage's Row Denizen

Whenever another blue creature you control enters, target player mills two cards.

Merfolk Mesmerist

Deprive

As an additional cost to cast this spell, return a land you control to its owner's hand.
Counter target spell.

Chilling Shade

Flying
{S}: Chilling Shade gets +1/+1 until end of turn. ({S} can be paid with one mana from a snow source.)

Destroy the Evidence

Destroy target land. Its controller reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.

Thought Scour

Target player mills two cards.
Draw a card.

Memory Sluice

Target player mills four cards.
Conspire (As you cast this spell, you may tap two untapped creatures you control that share a color with it. When you do, copy it and you may choose a new target for the copy.)

Tome Scour

Vision Charm

Choose one —
• Target player mills four cards.
• Choose a land type and a basic land type. Each land of the first chosen type becomes the second chosen type until end of turn.
• Target artifact 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.)

Chronic Flooding

Enchant land
Whenever enchanted land becomes tapped, its controller mills three cards.

Curse of the Bloody Tome

Enchant player
At the beginning of enchanted player's upkeep, that player mills two cards.

Induce Paranoia

Counter target spell. If {B} was spent to cast this spell, that spell's controller mills X cards, where X is the spell's mana value.

Iceberg Cancrix

Whenever another snow permanent you control enters, you may have target player mill two cards.

Pilfered Plans

Target player mills two cards. Draw two cards.

Winds of Rebuke

Return target nonland permanent to its owner's hand. Each player mills two cards.

Memory Lapse

Counter target spell. If that spell is countered this way, put it on top of its owner's library instead of into that player's graveyard.