Necrogen Mists

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

Guerrilla Tactics

Guerrilla Tactics deals 2 damage to any target.
When a spell or ability an opponent controls causes you to discard this card, it deals 4 damage to any target.

Chain of Plasma

Chain of Plasma deals 3 damage to any target. Then that player or that permanent's controller may discard a card. If the player does, they may copy this spell and may choose a new target for that copy.

Pure Intentions

Whenever a spell or ability an opponent controls causes you to discard cards this turn, return those cards from your graveyard to your hand.
When a spell or ability an opponent controls causes you to discard this card, return this card from your graveyard to your hand at the beginning of the next end step.

Chain of Smog

Target player discards two cards. That player may copy this spell and may choose a new target for that copy.

Psychic Purge

Psychic Purge deals 1 damage to any target.
When a spell or ability an opponent controls causes you to discard this card, that player loses 5 life.