Stormforged Armor 
Legendary Artifact — Equipment
Equipped creature has "Whenever this creature attacks, conjure a card named Ball Lightning onto the battlefield tapped and attacking." Equip—Pay 3 life.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyNOT LEGALvintageNOT LEGALcommanderNOT LEGAL