Oath of Liliana is a rare Legendary Enchantment card from Eldritch Moon (EMN), collector number 99. Current market price: $0.51 (foil $1.86), TCGplayer market prices via Scryfall.
When Oath of Liliana enters, each opponent sacrifices a creature of their choice. At the beginning of each end step, if a planeswalker entered the battlefield under your control this turn, create a 2/2 black Zombie creature token.