The Celestus is a rare Legendary Artifact card from Innistrad: Midnight Hunt Promos (PMID), collector number 252p. Current market price: $0.89 (foil $0.92), TCGplayer market prices via Scryfall.
If it's neither day nor night, it becomes day as The Celestus enters. {T}: Add one mana of any color. {3}, {T}: If it's night, it becomes day. Otherwise, it becomes night. Activate only as a sorcery. Whenever day becomes night or night becomes day, you gain 1 life. You may draw a card. If you do, discard a card.