Cheapest priced copy (World Championship Decks 1998): $10.99 at Card Kingdom, near mint, their price list as of .
Firestorm 
Instant · Rare · Weatherlight · #101
As an additional cost to cast this spell, discard X cards.
Firestorm deals X damage to each of X targets.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $10.99 to $39.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| World Championship Decks 1998 | br101sb | Rare | $14.99 | — |
| World Championship Decks 1998 | bs101 | Rare | $10.99 | — |
| Weatherlight | 101 | Rare | $39.99 | — |
3 rulings from Wizards of the Coast
- 1 April 2008For example, if you discard four cards, you must target four different creatures and/or players. Firestorm will deal 4 damage to each of them.
- 1 April 2008The 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.
- 1 April 2008The same permanent or player can’t be targeted more than once.