Silverquill, the Disputant is a mythic Legendary Creature — Elder Dragon card from Secrets of Strixhaven Promos (PSOS), collector number 226p. Current market price: $3.31 (foil $16.49), TCGplayer market prices via Scryfall.
Flying, vigilance Each instant and sorcery spell you cast has casualty 1. (As you cast that spell, you may sacrifice a creature with power 1 or greater. When you do, copy the spell and you may choose new targets for the copy.)