Firestorm | Magic: The Gathering
Formats Firestorm is Legal in
Official Oracle Text for Firestorm
Firestorm deals X damage to each of X target creatures and/or players.
—Squee, goblin cabin hand
Official Rulings for Firestorm
4/1/2008 : The value of X can't exceed the number of cards in your hand or the number of available legal targets, whichever is smaller. X can be 0.
4/1/2008 : The same creature or player can't be targeted more than once.