Duress

Target opponent reveals their hand. You choose a noncreature, nonland card from it. That player discards that card.

Drainpipe Vermin

When Drainpipe Vermin dies, you may pay {B}. If you do, target player discards a card.

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

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

When Burglar Rat enters, each opponent discards a card.

Target player draws two cards and loses 2 life.