Sorcery, XR (1) Fireball deals X damage divided evenly, rounded down, among any number of target creatures and/or players. Fireball costs {1} more to cast for each target beyond the first.1
Illus. Mark Tedin
12/1/2004: The additional cost is paid when you pay the rest of Fireball's costs, even though that text appears second on the card (to make the card easier to read). The additional cost doesn't count toward Fireball's converted mana cost.
12/1/2004: If, for example, X is 5 and you choose three target creatures, Fireball has a total cost of {7}{R} and it deals 1 damage to each of those three creatures.