Regal Sliver (CMM) from Commander Masters, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Victor Adame Minguez
• Card Text:
  Sliver creatures you control have "When this creature enters the battlefield, Slivers you control get +1/+1 until end of turn if you're the monarch. Otherwise, you become the monarch."