Liberator, Urza's Battlethopter is a rare Legendary Artifact Creature — Thopter card from The Brothers' War Promos (PBRO), collector number 237p. Current market price: $7.42 (foil $6.42), TCGplayer market prices via Scryfall.
Flash Flying You may cast colorless spells and artifact spells as though they had flash. Whenever you cast a spell, if the amount of mana spent to cast that spell is greater than Liberator's power, put a +1/+1 counter on Liberator.