Mystic Remora

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Maddening Cacophony

Kicker {3}{U}
Each opponent mills eight cards. If this spell was kicked, instead each opponent mills half their library, rounded up.

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.

Narset, Parter of Veils

Each opponent can't draw more than one card each turn.
−2: Look at the top four cards of your library. You may reveal a noncreature, nonland card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Dramatic Reversal

Untap all nonland permanents you control.

Negate

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.)

Thought Scour

Target player mills two cards.
Draw a card.

Fraying Sanity

Enchant player
At the beginning of each end step, enchanted player mills X cards, where X is the number of cards put into their graveyard from anywhere this turn.

Ambassador Laquatus

Thought Collapse

Counter target spell. Its controller mills three cards.

Anticognition

Counter target creature or planeswalker spell unless its controller pays {2}. If an opponent has eight or more cards in their graveyard, instead counter that spell, then scry 2.

Windfall

Each player discards their hand, then draws cards equal to the greatest number of cards a player discarded this way.

Baral, Chief of Compliance

Instant and sorcery spells you cast cost {1} less to cast.
Whenever a spell or ability you control counters a spell, you may draw a card. If you do, discard a card.

Sapphire Medallion

Blue spells you cast cost {1} less to cast.

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.

Essence Capture

Counter target creature spell. Put a +1/+1 counter on up to one target creature you control.

Counterspell

Micromancer

When this creature enters, you may search your library for an instant or sorcery card with mana value 1, reveal it, put it into your hand, then shuffle.

Terisian Mindbreaker

Whenever Terisian Mindbreaker attacks, defending player mills half their library, rounded up.
Unearth {1}{U}{U}{U} ({1}{U}{U}{U}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Isochron Scepter

Imprint — When Isochron Scepter enters, you may exile an instant card with mana value 2 or less from your hand.
{2}, {T}: You may copy the exiled card. If you do, you may cast the copy without paying its mana cost.

Visions of Beyond

Draw a card. If a graveyard has twenty or more cards in it, draw three cards instead.

Traumatize

Target player mills half their library, rounded down.

Mesmeric Orb

Whenever a permanent becomes untapped, that permanent's controller mills a card.

Mystical Tutor

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

Fleet Swallower

Whenever Fleet Swallower attacks, target player mills half their library, rounded up.