Scepter of Fugue

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

Horrifying Revelation

Target player discards a card, then mills a card.

Bottomless Pit

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

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.)

Liliana of the Veil

+1: Each player discards a card.
−2: Target player sacrifices a creature.
−6: Separate all permanents target player controls into two piles. That player sacrifices all permanents in the pile of their choice.

Surging Dementia

Ripple 4 (When you cast this spell, you may reveal the top four cards of your library. You may cast spells with the same name as this spell from among those cards without paying their mana costs. Put the rest on the bottom of your library.)
Target player discards a card.

Oppression

Whenever a player casts a spell, that player 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.

Stupor

Target opponent discards a card at random, then discards a card.

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, if it was kicked, target opponent discards two cards at random.

Words of Waste

{1}: The next time you would draw a card this turn, each opponent discards a card instead.

Strongarm Tactics

Each player discards a card. Then each player who didn't discard a creature card this way loses 4 life.

Sword of Feast and Famine

Equipped creature gets +2/+2 and has protection from black and from green.
Whenever equipped creature deals combat damage to a player, that player discards a card and you untap all lands you control.
Equip {2}

Braids's Frightful Return

Read ahead (Choose a chapter and start with that many lore counters. Add one after your draw step. Skipped chapters don't trigger. Sacrifice after III.)
I — You may sacrifice a creature. If you do, each opponent discards a card.
II — Return target creature card from your graveyard to your hand.
III — Target opponent may sacrifice a nonland, nontoken permanent of their choice. If they don't, they lose 2 life and you draw a card.

Cunning Lethemancer

At the beginning of your upkeep, each player discards a card.

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.

Vicious Rumors

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

Sangromancer

Flying
Whenever a creature an opponent controls dies, you may gain 3 life.
Whenever an opponent discards a card, you may gain 3 life.

Shrine of Limitless Power

At the beginning of your upkeep and whenever you cast a black spell, put a charge counter on Shrine of Limitless Power.
{4}, {T}, Sacrifice Shrine of Limitless Power: Target player discards a card for each charge counter on Shrine of Limitless Power.

Augur of Skulls

{1}{B}: Regenerate Augur of Skulls.
Sacrifice Augur of Skulls: Target player discards two cards. Activate only during your upkeep.

Liliana, Defiant Necromancer

+2: Each player discards a card.
−X: Return target nonlegendary creature card with mana value X from your graveyard to the battlefield.
−8: You get an emblem with "Whenever a creature dies, return it to the battlefield under your control at the beginning of the next end step."

Liliana, Heretical Healer

Lifelink
Whenever another nontoken creature you control dies, exile Liliana, Heretical Healer, then return her to the battlefield transformed under her owner's control. If you do, create a 2/2 black Zombie creature token.

Liliana, Heretical Healer // Liliana, Defiant Necromancer

Geth's Grimoire

Whenever an opponent discards a card, you may draw 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.

Triumph of Cruelty

At the beginning of your upkeep, target opponent discards a card if you control the creature with the greatest power or tied for the greatest power.

Hopeless Nightmare

When Hopeless Nightmare enters, each opponent discards a card and loses 2 life.
When Hopeless Nightmare is put into a graveyard from the battlefield, scry 2.
{2}{B}: Sacrifice Hopeless Nightmare.

Torment of Hailfire

Repeat the following process X times. Each opponent loses 3 life unless that player sacrifices a nonland permanent of their choice or discards a card.

Forbidden Ritual

Sacrifice a nontoken permanent. If you do, target opponent loses 2 life unless that player sacrifices a permanent of their choice or discards a card. You may repeat this process any number of times.

Unhinge

Target player discards a card.
Draw a card.

Raven's Crime

Target player discards a card.
Retrace (You may cast this card from your graveyard by discarding a land card in addition to paying its other costs.)

Mind Peel

Buyback {2}{B}{B} (You may pay an additional {2}{B}{B} as you cast this spell. If you do, put this card into your hand as it resolves.)
Target player discards a card.

Pulling Teeth

Clash with an opponent. If you win, target player discards two cards. Otherwise, that player discards a card. (Each clashing player reveals the top card of their library, then puts that card on the top or bottom. A player wins if their card had a higher mana value.)

Chilling Apparition

{B}: Regenerate Chilling Apparition.
Whenever Chilling Apparition deals combat damage to a player, that player discards a card.

Swamp

Tar Fiend

Devour 2 (As this enters, you may sacrifice any number of creatures. This creature enters with twice that many +1/+1 counters on it.)
When Tar Fiend enters, target player discards a card for each creature it devoured.

Mind Ravel

Target player discards a card.
Draw a card at the beginning of the next turn's upkeep.

Hypnotic Specter

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

Sink into Takenuma

Sweep — Return any number of Swamps you control to their owner's hand. Target player discards a card for each Swamp returned this way.

Liliana's Caress

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

Abyssal Specter

Flying
Whenever Abyssal Specter deals damage to a player, that player discards a card.