Theorist's Proxy is a rare Creature — Illusion card from Reality Fracture (FRA), collector number 339. Current market price: $0.35 (foil $0.91), TCGplayer market prices via Scryfall.
Flash When this creature enters, empower Jace 3. (Put three loyalty counters on a Jace token you control. If you don't control one, first create a blue Jace planeswalker token with "[−1]: Surveil 1" and "[−3]: Draw a card.") {U}, Sacrifice this creature: The next spell you cast this turn can't be countered.