Geth's Grimoire

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

Soul Shatter

Each opponent sacrifices a creature or planeswalker with the highest mana value among creatures and planeswalkers they control.

Liliana, Waker of the Dead

+1: Each player discards a card. Each opponent who can't loses 3 life.
−3: Target creature gets -X/-X until end of turn, where X is the number of cards in your graveyard.
−7: You get an emblem with "At the beginning of combat on your turn, put target creature card from a graveyard onto the battlefield under your control. It gains haste."

Sadistic Hypnotist

Sacrifice a creature: Target player discards two cards. Activate only as a sorcery.

Scythe Specter

Flying
Whenever Scythe Specter deals combat damage to a player, each opponent discards a card. Each player who discarded a card with the highest mana value among cards discarded this way loses life equal to that mana value.

Liliana's Specter

Flying
When Liliana's Specter enters, each opponent discards a card.

Mire in Misery

Each opponent sacrifices a creature or enchantment.

Blighted Fen

{T}: Add {C}.
{4}{B}, {T}, Sacrifice Blighted Fen: Target opponent sacrifices a creature.

Bottomless Pit

At the beginning of each player's upkeep, that player discards a card at random.

Dark Ritual

Syphon Mind

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

Court of Ambition

When Court of Ambition enters, you become the monarch.
At the beginning of your upkeep, each opponent loses 3 life unless they discard a card. If you're the monarch, instead each opponent loses 6 life unless they discard two cards.