Blue Sun's Twilight is a rare Sorcery card from Phyrexia: All Will Be One Promos (PONE), collector number 43p. Current market price: $0.62 (foil $0.74), TCGplayer market prices via Scryfall.
Gain control of target creature with mana value X or less. If X is 5 or more, create a token that's a copy of that creature.