Exhibition Tidecaller is a rare Creature — Djinn Wizard card from Secrets of Strixhaven (SOS), collector number 316. Current market price: $1.41 (foil $1.68), TCGplayer market prices via Scryfall.
Opus — Whenever you cast an instant or sorcery spell, target player mills three cards. If five or more mana was spent to cast that spell, that player mills ten cards instead.