Memory Erosion

Whenever an opponent casts a spell, that player mills two cards.

Sakashima of a Thousand Faces

You may have Sakashima of a Thousand Faces enter as a copy of another creature you control, except it has Sakashima of a Thousand Faces's other abilities.
The "legend rule" doesn't apply to permanents you control.
Partner (You can have two commanders if both have partner.)

Windfall

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

Jace's Archivist

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

Island

Jace Beleren

+2: Each player draws a card.
−1: Target player draws a card.
−10: Target player mills twenty cards.

Persistent Petitioners

{1}, {T}: Target player mills a card. (They put the top card of their library into their graveyard.)
Tap four untapped Advisors you control: Target player mills twelve cards.
A deck can have any number of cards named Persistent Petitioners.

Maddening Cacophony

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

Into the Story

This spell costs {3} less to cast if an opponent has seven or more cards in their graveyard.
Draw four cards.

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.)

Distant Melody

Choose a creature type. Draw a card for each permanent you control of that type.

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.

Herald's Horn

As Herald's Horn enters, choose a creature type.
Creature spells you cast of the chosen type cost {1} less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

Mesmeric Orb

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

Rhystic Study

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

Kefnet's Monument

Blue creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, target creature an opponent controls doesn't untap during its controller's next untap step.

Tasha's Hideous Laughter

Each opponent exiles cards from the top of their library until that player has exiled cards with total mana value 20 or more.

Psychic Corrosion

Whenever you draw a card, each opponent mills two cards.

Mass Appeal

Patchwork Banner

As Patchwork Banner enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
{T}: Add one mana of any color.

Spark Double

You may have Spark Double enter as a copy of a creature or planeswalker you control, except it enters with an additional +1/+1 counter on it if it's a creature, it enters with an additional loyalty counter on it if it's a planeswalker, and it isn't legendary.

Sapphire Medallion

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

Quantum Misalignment

Create a token that's a copy of target creature you control, except it isn't legendary.
Rebound (If you cast this spell from your hand, exile it as it resolves. At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.)

Fractured Sanity

Each opponent mills fourteen cards.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)
When you cycle Fractured Sanity, each opponent mills four cards.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Visions of Beyond

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