Bitterblossom is a mythic Kindred Enchantment — Faerie card from Special Guests (SPG), collector number 133. Current market price: $31.58 (foil $35.07), TCGplayer market prices via Scryfall.
At the beginning of your upkeep, you lose 1 life and create a 1/1 black Faerie Rogue creature token with flying.