The Cauldron of Eternity is a mythic Legendary Artifact card from Throne of Eldraine Promos (PELD), collector number 82s. Current market price: — (foil $3.45), TCGplayer market prices via Scryfall.
This spell costs {2} less to cast for each creature card in your graveyard. Whenever a creature you control dies, put it on the bottom of its owner's library. {2}{B}, {T}, Pay 2 life: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.