Thryx, the Sudden Storm is a rare Legendary Creature — Elemental Giant card from Theros Beyond Death Promos (PTHB), collector number 76p. Current market price: $0.81 (foil $0.59), TCGplayer market prices via Scryfall.
Flash (You may cast this spell any time you could cast an instant.) Flying Spells you cast with mana value 5 or greater cost {1} less to cast and can't be countered.