Norn's Decree is a rare Enchantment card from Phyrexia: All Will Be One Commander (ONC), collector number 47. Current market price: $8.34, TCGplayer market prices via Scryfall.
Whenever one or more creatures an opponent controls deal combat damage to you, that opponent gets a poison counter. Whenever a player attacks, if one or more players being attacked are poisoned, the attacking player draws a card.