Kassa, The Dissidant

Whenever you cast an Instant or Sorcery, target
player discards a card. Then, draw 1.
Whenever a card is drawn or discarded due
to the effect of Kassa, The Dissident, you may
pay {p/b}{p/u}. If you do, return target Instant
or Sorcery card from your graveyard to your
hand.