Theorist's Sanctum is a rare Land — Island card from Reality Fracture (FRA), collector number 381. Current market price: $0.68 (foil $3.05), TCGplayer market prices via Scryfall.
({T}: Add {U}.) As this land enters, you may behold a Jace. If you don't, this land enters tapped. (To behold a Jace, choose a Jace you control or reveal a Jace card from your hand.) {2}{U}, {T}: Empower Jace 2.