Inferno of the Star Mounts is a mythic Legendary Creature — Dragon card from Adventures in the Forgotten Realms (AFR), collector number 151. Current market price: $3.30 (foil $3.13), TCGplayer market prices via Scryfall.
This spell can't be countered. Flying, haste {R}: Inferno of the Star Mounts gets +1/+0 until end of turn. When its power becomes 20 this way, it deals 20 damage to any target.