Karlov's Crossbow 
Artifact — Equipment
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.)
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyNOT LEGALvintageNOT LEGALcommanderNOT LEGAL