Boros Keyrune (GTC) from Gatecrash, available at 401 Games Canada.

• Rarity: Uncommon
• Finish: Normal
• Artist: Daniel Ljunggren
• Card Text:
  T: Add R or W to your mana pool.
  RW: Boros Keyrune becomes a 1/1 red and white Soldier artifact creature with double strike until end of turn. (It deals both first-strike and regular combat damage.)