Horrifying Revelation

Target player discards a card, then mills a card.

Miasmic Mummy

When Miasmic Mummy enters the battlefield, each player discards a card.

The Raven Man

At the beginning of each end step, if a player discarded a card this turn, create a 1/1 black Bird creature token with flying and "This creature can't block."
{3}{B}, {T}: Each opponent discards a card. Activate only as a sorcery.

Cry of Contrition

Target player discards a card.
Haunt (When this spell card is put into a graveyard after resolving, exile it haunting target creature.)
When the creature Cry of Contrition haunts dies, target player discards a card.

Vicious Rumors

Vicious Rumors deals 1 damage to each opponent. Each opponent discards a card, then mills a card. You gain 1 life.

Abyssal Nocturnus

Whenever an opponent discards a card, Abyssal Nocturnus gets +2/+2 and gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)

Tendrils of Despair

As an additional cost to cast this spell, sacrifice a creature.
Target opponent discards two cards.

Tourach, Dread Cantor

Kicker {B}{B} (You may pay an additional {B}{B} as you cast this spell.)
Protection from white
Whenever an opponent discards a card, put a +1/+1 counter on Tourach, Dread Cantor.
When Tourach enters the battlefield, if it was kicked, target opponent discards two cards at random.

Hypnotic Cloud

Kicker {4} (You may pay an additional {4} as you cast this spell.)
Target player discards a card. If this spell was kicked, that player discards three cards instead.

Ravenous Rats

When Ravenous Rats enters the battlefield, target opponent discards a card.

Harsh Scrutiny

Target opponent reveals their hand. You choose a creature card from it. That player discards that card. Scry 1.

Deadbridge Shaman

When Deadbridge Shaman dies, target opponent discards a card.

Psychic Miasma

Target player discards a card. If a land card is discarded this way, return Psychic Miasma to its owner's hand.

Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Specter's Wail

Divest

Target player reveals their hand. You choose an artifact or creature card from it. That player discards that card.

God-Eternal Kefnet

Flying
You may reveal the first card you draw each turn as you draw it. Whenever you reveal an instant or sorcery card this way, copy that card and you may cast the copy. That copy costs {2} less to cast.
When God-Eternal Kefnet dies or is put into exile from the battlefield, you may put it into its owner's library third from the top.

Liliana's Steward

{T}, Sacrifice Liliana's Steward: Target opponent discards a card. Activate only as a sorcery.

Elvish Doomsayer

When Elvish Doomsayer dies, each opponent discards a card.

Corrupt Court Official

When Corrupt Court Official enters the battlefield, target opponent discards a card.

Black Cat

When Black Cat dies, target opponent discards a card at random.

Despise

Target opponent reveals their hand. You choose a creature or planeswalker card from it. That player discards that card.

Swamp

Drainpipe Vermin

When Drainpipe Vermin dies, you may pay {B}. If you do, target player discards a card.

Nezumi Bone-Reader

{B}, Sacrifice a creature: Target player discards a card. Activate only as a sorcery.

Bloodhusk Ritualist

Multikicker {B} (You may pay an additional {B} any number of times as you cast this spell.)
When Bloodhusk Ritualist enters the battlefield, target opponent discards a card for each time it was kicked.

Nezumi Informant

When Nezumi Informant enters the battlefield, each opponent discards a card.

Whispers of Emrakul

Target opponent discards a card at random.
Delirium — If there are four or more card types among cards in your graveyard, that player discards two cards at random instead.

Virus Beetle

When Virus Beetle enters the battlefield, each opponent discards a card.

Elderfang Disciple

When Elderfang Disciple enters the battlefield, each opponent discards a card.

Blackmail

Target player reveals three cards from their hand and you choose one of them. That player discards that card.