Oppression

Whenever a player casts a spell, that player discards a card.

Cunning Lethemancer

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

Stronghold Rats

Shadow (This creature can block or be blocked by only creatures with shadow.)
Whenever this creature deals combat damage to a player, each player discards a card.

Bottomless Pit

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

Creeping Dread

At the beginning of your upkeep, each player discards a card. Each opponent who discarded a card that shares a card type with the card you discarded loses 3 life. (Players reveal the discarded cards simultaneously.)

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.

Vicious Rumors

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

Miasmic Mummy

When this creature enters, each player discards a card.

Sibsig Icebreakers

Burglar Rat

When this creature enters, each opponent discards a card.

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

Smallpox

Each player loses 1 life, discards a card, sacrifices a creature of their choice, then sacrifices a land of their choice.

Blightning

Blightning deals 3 damage to target player or planeswalker. That player or that planeswalker's controller discards two cards.

Pain Magnification

Whenever an opponent is dealt 3 or more damage by a single source, that player discards a card.

Memory Jar

{T}, Sacrifice this artifact: Each player exiles all cards from their hand face down and draws seven cards. At the beginning of the next end step, each player discards their hand and returns to their hand each card they exiled 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.

Hypnotic Specter

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

Painful Quandary

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

Sire of Insanity

At the beginning of each end step, each player discards their hand.

Noxious Vapors

Each player reveals their hand, chooses one card of each color from it, then discards all other nonland cards.

Strongarm Tactics

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

Arterial Flow

Each opponent discards two cards. If you control a Vampire, each opponent loses 2 life and you gain 2 life.

Dreamstealer

Menace
Whenever this creature deals combat damage to a player, that player discards that many cards.
Eternalize {4}{B}{B} ({4}{B}{B}, Exile this card from your graveyard: Create a token that's a copy of it, except it's a 4/4 black Zombie Human Wizard with no mana cost. Eternalize only as a sorcery.)

Rotting Rats

When this creature enters, each player discards a card.
Unearth {1}{B} ({1}{B}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Anvil of Bogardan

Players have no maximum hand size.
At the beginning of each player's draw step, that player draws an additional card, then discards a card.

Scandalmonger

{2}: Target player discards a card. Any player may activate this ability but only as a sorcery.

Guul Draz Specter

Flying
This creature gets +3/+3 as long as an opponent has no cards in hand.
Whenever this creature deals combat damage to a player, that player discards a card.

Fell Specter

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