Bitter Feud (CM2) from Commander Anthology Volume II, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Aaron Miller
• Card Text:
  As Bitter Feud enters the battlefield, choose two players.
  If a source controlled by one of the chosen players would deal damage to the other chosen player or a permanent that player controls, that source deals double that damage to that player or permanent instead.