Porphyry Nodes (PLC) from Planar Chaos, available at 401 Games Canada.

• Rarity: Rare
• Finish: Normal
• Artist: Alan Pollack
• Card Text:
  At the beginning of your upkeep, destroy the creature with the least power. It can't be regenerated. If two or more creatures are tied for least power, you choose one of them.
  When there are no creatures in play, sacrifice Porphyry Nodes.