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.

Liliana's Caress

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

Feast of Sanity

Whenever you discard a card, Feast of Sanity deals 1 damage to any target and you gain 1 life.

Waste Not

Whenever an opponent discards a creature card, create a 2/2 black Zombie creature token.
Whenever an opponent discards a land card, add {B}{B}.
Whenever an opponent discards a noncreature, nonland card, draw a card.

Forbid

Buyback—Discard two cards. (You may discard two cards in addition to any other costs as you cast this spell. If you do, put this card into your hand as it resolves.)
Counter target spell.

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Recycle

Skip your draw step.
Whenever you play a card, draw a card.
Your maximum hand size is two.

Oskar, Rubbish Reclaimer

This spell costs {1} less to cast for each different mana value among cards in your graveyard.
Whenever you discard a nonland card, you may cast it from your graveyard.

Painful Quandary

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

Arcane Signet

Mystic Redaction

At the beginning of your upkeep, scry 1.
Whenever you discard a card, each opponent mills two cards. (They put the top two cards of their library into their graveyard.)

Damia, Sage of Stone

Deathtouch
Skip your draw step.
At the beginning of your upkeep, if you have fewer than seven cards in hand, draw cards equal to the difference.

Bone Miser

Whenever you discard a creature card, create a 2/2 black Zombie creature token.
Whenever you discard a land card, add {B}{B}.
Whenever you discard a noncreature, nonland card, draw a card.

Psychic Corrosion

Whenever you draw a card, each opponent mills two cards.

Bone Shards

As an additional cost to cast this spell, sacrifice a creature or discard a card.
Destroy target creature or planeswalker.

Dawnstrider

{G}, {T}, Discard a card: Prevent all combat damage that would be dealt this turn.

Oppression

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

Teferi's Ageless Insight

If you would draw a card except the first one you draw in each of your draw steps, draw two cards instead.

Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

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.)

Splendid Reclamation

Return all land cards from your graveyard to the battlefield tapped.

Llanowar Mentor

{G}, {T}, Discard a card: Create a 1/1 green Elf Druid creature token named Llanowar Elves. It has "{T}: Add {G}."