Bottomless Pit

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

Hollowsage

Whenever Hollowsage becomes untapped, you may have target player discard a card.

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.

Fatal Push

Destroy target creature if it has mana value 2 or less.
Revolt — Destroy that creature if it has mana value 4 or less instead if a permanent you controlled left the battlefield this turn.

Megrim

Whenever an opponent discards a card, Megrim deals 2 damage to that player.

Shrieking Affliction

At the beginning of each opponent's upkeep, if that player has one or fewer cards in hand, they lose 3 life.

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Tyrannize

Target player discards their hand unless they pay 7 life.

Dream Salvage

Draw cards equal to the number of cards target opponent discarded this turn.