Soul Tithe is a uncommon Enchantment — Aura card from Return to Ravnica (RTR), collector number 23. Current market price: $0.18 (foil $0.43), TCGplayer market prices via Scryfall.
Enchant nonland permanent At the beginning of the upkeep of enchanted permanent's controller, that player sacrifices it unless they pay {X}, where X is its mana value.