Megrim

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

Greel, Mind Raker

{X}{B}, {T}, Discard two cards: Target player discards X cards at random.

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.

Grim Strider

Grim Strider gets -1/-1 for each card in your hand.

Davriel, Rogue Shadowmage

At the beginning of each opponent's upkeep, if that player has one or fewer cards in hand, Davriel, Rogue Shadowmage deals 2 damage to them.
−1: Target player discards a card.