Door of Destinies is a mythic Artifact card from Special Guests (SPG), collector number 146. Current market price: $9.36 (foil $13.30), TCGplayer market prices via Scryfall.
As this artifact enters, choose a creature type. Whenever you cast a spell of the chosen type, put a charge counter on this artifact. Creatures you control of the chosen type get +1/+1 for each charge counter on this artifact.