Liliana's Caress

Whenever an opponent discards a card, that player loses 2 life.

Mental Vapors

Target player discards a card.
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.)

Bite of the Black Rose

Will of the council — Starting with you, each player votes for sickness or psychosis. If sickness gets more votes, creatures your opponents control get -2/-2 until end of turn. If psychosis gets more votes or the vote is tied, each opponent discards two cards.

Tinybones, Trinket Thief

At the beginning of each end step, if an opponent discarded a card this turn, you draw a card and you lose 1 life.
{4}{B}{B}: Each opponent with no cards in hand loses 10 life.

Davriel, Rogue Shadowmage

At the beginning of each opponent's upkeep, if that player has one or fewer cards in hand, Davriel, Rogue Shadowmage deals 2 damage to them.
−1: Target player discards a card.

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.)

Noggin Whack

Prowl {1}{B} (You may cast this for its prowl cost if you dealt combat damage to a player this turn with a Rogue.)
Target player reveals three cards from their hand. You choose two of them. That player discards those cards.

Swamp

Oona's Prowler

Flying
Discard a card: Oona's Prowler gets -2/-0 until end of turn. Any player may activate this ability.

Scepter of Fugue

{1}{B}, {T}: Target player discards a card. Activate only during your turn.

Thoughtseize

Target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

Peer into the Abyss

Target player draws cards equal to half the number of cards in their library and loses half their life. Round up each time.

Cao Cao, Lord of Wei

{T}: Target opponent discards two cards. Activate only during your turn, before attackers are declared.

Duress

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

The Haunt of Hightower

Flying, lifelink
Whenever The Haunt of Hightower attacks, defending player discards a card.
Whenever a card is put into an opponent's graveyard from anywhere, put a +1/+1 counter on The Haunt of Hightower.

Persecute

Choose a color. Target player reveals their hand and discards all cards of that color.

Hymn to Tourach

Target player discards two cards at random.

Megrim

Whenever an opponent discards a card, Megrim deals 2 damage to that player.

Geth's Grimoire

Whenever an opponent discards a card, you may draw a card.

Davriel's Shadowfugue

Target player discards two cards and loses 2 life.

Undercity Plague

Target player loses 1 life, discards a card, then sacrifices a permanent of their choice.
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.)

Wrench Mind

Target player discards two cards unless they discard an artifact card.

Myojin of Night's Reach

Myojin of Night's Reach enters with a divinity counter on it if you cast it from your hand.
Myojin of Night's Reach has indestructible as long as it has a divinity counter on it.
Remove a divinity counter from Myojin of Night's Reach: Each opponent discards their hand.

Distress

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

Mindslicer

When Mindslicer dies, each player discards their hand.

Remorseless Punishment

Target opponent loses 5 life unless that player discards two cards or sacrifices a creature or planeswalker of their choice. Repeat this process once.

Waste Not

Whenever an opponent discards a creature card, create a 2/2 black Zombie creature token.
Whenever an opponent discards a land card, add {B}{B}.
Whenever an opponent discards a noncreature, nonland card, draw a card.