Painful Quandary

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

Ravenous Rats

When Ravenous Rats enters, target opponent discards a card.

Nezumi Bone-Reader

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

Swamp

Liliana's Caress

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

Megrim

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

Harsh Scrutiny

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

Quest for the Nihil Stone

Whenever an opponent discards a card, you may put a quest counter on Quest for the Nihil Stone.
At the beginning of each opponent's upkeep, if that player has no cards in hand and Quest for the Nihil Stone has two or more quest counters on it, you may have that player lose 5 life.

Inquisition of Kozilek

Target player reveals their hand. You choose a nonland card from it with mana value 3 or less. That player discards that card.

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.

Geth's Grimoire

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

Hymn to Tourach

Target player discards two cards at random.

Hypnotic Specter

Flying
Whenever Hypnotic Specter deals damage to an opponent, that player discards a card at random.

The Rack

As The Rack enters, choose an opponent.
At the beginning of the chosen player's upkeep, The Rack deals X damage to that player, where X is 3 minus the number of cards in their hand.

Distress

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