Hellkite Charger (ARC) from Archenemy, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Jaime Jones
• Card Text:
  Flying, haste
  Whenever Hellkite Charger attacks, you may pay 5RR. If you do, untap all attacking creatures and after this phase, there is an additional combat phase.