Each booster box contains 24 packs of 15 random cards. Second limited print run. Released on June 11, 2020. Mystery Boosters contain 15 cards. ... Each Convention pack has 2 commons/uncommons of each color, 1 multicolored common/uncommon, 1 common/uncommon artifact/land, 1 special slot, 1 rare/mythic rare with the M15 card frame and one pre-M15 card in its original frame.