Cheapest priced copy (Archenemy): $0.35 at Card Kingdom, near mint, their price list as of .
Inferno Trap 
Instant — Trap · Uncommon · Archenemy · #43
If you've been dealt damage by two or more creatures this turn, you may pay {R} rather than pay this spell's mana cost.
Inferno Trap deals 4 damage to target creature.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Archenemy | 43 | Uncommon | $0.35 | — |
| Duel Decks: Speed vs. Cunning | 67 | Uncommon | $0.35 | — |
| Zendikar | 133 | Uncommon | $0.35 | $0.49 |
7 rulings from Wizards of the Coast
- 1 October 2009You may ignore a Trap's alternative cost condition and simply cast it for its normal mana cost. This is true even if its alternative cost condition has been met.
- 1 October 2009You may target any creature, not just one that dealt damage to you this turn.
- 1 October 2009Inferno Trap's alternative cost condition checks for any damage, not just combat damage.
- 1 October 2009The alternative cost condition is satisfied only if two different creatures dealt damage to you, not if one creature dealt damage to you twice. The damage may have been dealt to you simultaneously (as with combat damage), or at separate times.
- 1 October 2009The alternative cost condition doesn't check who controlled the creatures that dealt damage to you. Damage dealt to you by your own creatures counts.
- 1 October 2009Casting a Trap by paying its alternative cost doesn't change its mana cost or mana value. The only difference is the cost you actually pay.
- 1 October 2009Effects that increase or reduce the cost to cast a Trap will apply to whichever cost you chose to pay.