Nyx Lotus is a rare Legendary Artifact card from Theros Beyond Death Promos (PTHB), collector number 235p. Current market price: $5.99 (foil $6.54), TCGplayer market prices via Scryfall.
Nyx Lotus enters tapped. {T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)