Porphyry Nodes is a rare Enchantment card from Planar Chaos (PLC), collector number 28. Current market price: $0.77 (foil $8.03), TCGplayer market prices via Scryfall.
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 on the battlefield, sacrifice this enchantment.