Stenn, Paranoid Partisan is a rare Legendary Creature — Human Wizard card from Dominaria United Promos (PDMU), collector number 221p. Current market price: $0.36 (foil $0.37), TCGplayer market prices via Scryfall.
As Stenn enters, choose a card type other than creature or land. Spells you cast of the chosen type cost {1} less to cast. {1}{W}{U}: Exile Stenn. Return it to the battlefield under its owner's control at the beginning of the next end step.