Karlov's Crossbow (DA1-CA06A) - Unknown Event

Whenever equipped creature attacks, sacrifice Karlov's Crossbow and destroy target creature an opponent controls.
Equip
Forecast — , Reveal Karlov's Crossbow from your hand: For the remainder of the game, spells you cast named Karlov's Crossbow cost less to cast. (Activate only during your upkeep and only once each turn.)