Megrim

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

Liliana's Caress

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

Vicious Rumors

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

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.

Village Rites

As an additional cost to cast this spell, sacrifice a creature.
Draw two cards.

Virus Beetle

When this creature enters, each opponent discards a card.

Nezumi Informant

Painful Quandary

Whenever an opponent casts a spell, that player loses 5 life unless they discard a card.

Burglar Rat

Necrogoyf

Necrogoyf's power is equal to the number of creature cards in all graveyards.
At the beginning of each player's upkeep, that player discards a card.
Madness {1}{B}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Syphon Mind

Each other player discards a card. You draw a card for each card discarded this way.

Raiders' Wake

Whenever an opponent discards a card, that player loses 2 life.
Raid — At the beginning of your end step, if you attacked this turn, target opponent discards a card.

Elderfang Disciple

Fell Specter

Flying
When this creature enters, target opponent discards a card.
Whenever an opponent discards a card, that player loses 2 life.

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 token can't block."
{3}{B}, {T}: Each opponent discards a card. Activate only as a sorcery.