Geth's Grimoire

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

Dreamstealer

Menace
Whenever Dreamstealer 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.)

Curse of Chaos

Enchant player
Whenever a player attacks enchanted player with one or more creatures, that attacking player may discard a card. If the player does, they draw a card.

Glint-Horn Buccaneer

Haste
Whenever you discard a card, Glint-Horn Buccaneer deals 1 damage to each opponent.
{1}{R}, Discard a card: Draw a card. Activate only if Glint-Horn Buccaneer is attacking.

Dokuchi Silencer

Ninjutsu {1}{B} ({1}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Dokuchi Silencer deals combat damage to a player, you may discard a creature card. When you do, destroy target creature or planeswalker that player controls.

Neheb, Dreadhorde Champion

Trample
Whenever Neheb, Dreadhorde Champion deals combat damage to a player or planeswalker, you may discard any number of cards. If you do, draw that many cards and add that much {R}. Until end of turn, you don't lose this mana as steps and phases end.

Imposing Grandeur

Each player may discard their hand and draw cards equal to the greatest mana value of a commander they own on the battlefield or in the command zone.

Hypnotic Specter

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

Larceny

Whenever a creature you control deals combat damage to a player, that player discards a card.

Angrath, the Flame-Chained

+1: Each opponent discards a card and loses 2 life.
−3: Gain control of target creature until end of turn. Untap it. It gains haste until end of turn. Sacrifice it at the beginning of the next end step if it has mana value 3 or less.
−8: Each opponent loses life equal to the number of cards in their graveyard.

Liliana's Reaver

Deathtouch
Whenever Liliana's Reaver deals combat damage to a player, that player discards a card and you create a tapped 2/2 black Zombie creature token.

Containment Construct

Whenever you discard a card, you may exile that card from your graveyard. If you do, you may play that card this turn.

Ashiok's Adept

Heroic — Whenever you cast a spell that targets Ashiok's Adept, each opponent discards a card.

Chainer, Nightmare Adept

Discard a card: You may cast a creature spell from your graveyard this turn. Activate only once each turn.
Whenever a nontoken creature enters the battlefield under your control, if you didn't cast it from your hand, it gains haste until your next turn.

Barbed Shocker

Trample, haste
Whenever Barbed Shocker deals damage to a player, that player discards all the cards in their hand, then draws that many cards.

Fell Specter

Flying
When Fell Specter enters the battlefield, target opponent discards a card.
Whenever an opponent discards a card, that player loses 2 life.

Dragon Mage

Flying
Whenever Dragon Mage deals combat damage to a player, each player discards their hand, then draws seven cards.

Anje Falkenrath

Haste
{T}, Discard a card: Draw a card.
Whenever you discard a card, if it has madness, untap Anje Falkenrath.

Archfiend of Ifnir

Flying
Whenever you cycle or discard another card, put a -1/-1 counter on each creature your opponents control.
Cycling {2} ({2}, Discard this card: Draw a card.)

Currency Converter

Whenever you discard a card, you may exile that card from your graveyard.
{2}, {T}: Draw a card, then discard a card.
{T}: Put a card exiled with Currency Converter into your graveyard. If it's a land card, create a Treasure token. If it's a nonland card, create a 2/2 black Rogue creature token.

Dying to Serve

Whenever you discard one or more cards, create a tapped 2/2 black Zombie creature token. This ability triggers only once each turn.

Mask of Memory

Whenever equipped creature deals combat damage to a player, you may draw two cards. If you do, discard a card.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)