Door of Destinies is a rare Artifact card from Commander 2017 (C17), collector number 208. Current market price: $6.09, 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.