The Fifteenth Doctor is a rare Legendary Creature — Time Lord Doctor card from Secret Lair Drop (SLD), collector number 1584. Current market price: $34.92 (foil $35.68), TCGplayer market prices via Scryfall.
Whenever The Fifteenth Doctor enters or attacks, mill three cards. You may put an artifact card with mana value 2 or 3 from among them into your hand. The first nonartifact spell you cast each turn has improvise. (Your artifacts can help cast that spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)