Exhibition Tidecaller is a rare Creature — Djinn Wizard card from Secrets of Strixhaven Promos (PSOS), collector number 48p. Current market price: $1.50 (foil $3.79), 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.