Thunder of Unity is a rare Enchantment — Saga card from Tarkir: Dragonstorm Promos (PTDM), collector number 231p. Current market price: $0.25 (foil $0.71), TCGplayer market prices via Scryfall.
(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.) I — You draw two cards and you lose 2 life. II, III — Whenever a creature you control enters this turn, each opponent loses 1 life and you gain 1 life.