Chill of Foreboding

Each player mills five cards.
Flashback {7}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Thought Collapse

Counter target spell. Its controller mills three cards.

Altar of the Brood

Whenever another permanent you control enters, each opponent mills a card.

Mind Sculpt

Drowner of Secrets

Tap an untapped Merfolk you control: Target player mills a card.

Psychic Spiral

Shuffle all cards from your graveyard into your library. Target player mills that many cards.

Codex Shredder

{T}: Target player mills a card. (They put the top card of their library into their graveyard.)
{5}, {T}, Sacrifice Codex Shredder: Return target card from your graveyard to your hand.

Altar of Dementia

Sacrifice a creature: Target player mills cards equal to the sacrificed creature's power.

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.)

Thassa's Bounty

Draw three cards. Target player mills three cards.

Countermand

Counter target spell. Its controller mills four cards.

Tome Scour

Merrow Witsniper

When Merrow Witsniper enters, target player mills a card.

Moonring Island

({T}: Add {U}.)
Moonring Island enters tapped.
{U}, {T}: Look at the top card of target player's library. Activate only if you control two or more blue permanents.

Folio of Fancies

Players have no maximum hand size.
{X}{X}, {T}: Each player draws X cards.
{2}{U}, {T}: Each opponent mills cards equal to the number of cards in their hand.

Weight of Memory

Compelling Argument

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

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.)

Jace, the Perfected Mind

Compleated ({U/P} can be paid with {U} or 2 life. If life was paid, this planeswalker enters with two fewer loyalty counters.)
+1: Until your next turn, up to one target creature gets -3/-0.
−2: Target player mills three cards. Then if a graveyard has twenty or more cards in it, you draw three cards. Otherwise, you draw a card.
−X: Target player mills three times X cards.

Traumatize

Target player mills half their library, rounded down.

Ambassador Laquatus

Island

Mindcrank

Whenever an opponent loses life, that player mills that many cards. (Damage causes loss of life.)

Millstone

Cathartic Adept

Sanity Grinding

Chroma — Reveal the top ten cards of your library. For each blue mana symbol in the mana costs of the revealed cards, target opponent mills a card. Then put the cards you revealed this way on the bottom of your library in any order.

Bruvac the Grandiloquent

If an opponent would mill one or more cards, they mill twice that many cards instead. (To mill a card, a player puts the top card of their library into their graveyard.)

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.)

Didn't Say Please

Sweet Oblivion

Target player mills four cards.
Escape—{3}{U}, Exile four other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Glacial Grasp

Tap target creature. Its controller mills two cards. That creature doesn't untap during its controller's next untap step. (They put the top two cards of their library into their graveyard.)
Draw a card.

Bond of Insight

Each player mills four cards. Return up to two instant and/or sorcery cards from your graveyard to your hand. Exile Bond of Insight.

Merfolk Windrobber

Flying
Whenever Merfolk Windrobber deals combat damage to a player, that player mills a card. (They put the top card of their library into their graveyard.)
Sacrifice Merfolk Windrobber: Draw a card. Activate only if an opponent has eight or more cards in their graveyard.

Cut Your Losses

Casualty 2 (As you cast this spell, you may sacrifice a creature with power 2 or greater. When you do, copy this spell and you may choose a new target for the copy.)
Target player mills half their library, rounded down.

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

Hedron Crab

Landfall — Whenever a land you control enters, target player mills three cards.