Inferno Trap (ARC) from Archenemy, available at 401 Games Canada.

• Rarity: Uncommon
• Finish: Normal
• Artist: Philip Straub
• Card Text:
  If you've been dealt damage by two or more creatures this turn, you may pay R rather than pay Inferno Trap's mana cost.
  Inferno Trap deals 4 damage to target creature.