Roar of Endless Song is a rare Enchantment — Saga card from Tarkir: Dragonstorm Promos (PTDM), collector number 220p. Current market price: $0.36 (foil $0.20), TCGplayer market prices via Scryfall.
(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.) I, II — Create a 5/5 green Elephant creature token. III — Double the power and toughness of each creature you control until end of turn.