X is a rare Legendary Creature — Human Spy card from Unstable (UST), collector number 137. Current market price: $0.36 (foil $2.93), TCGplayer market prices via Scryfall.
As long as X is in X's owner's opponent's hand, X's owner may cast X and activate X's abilities. That opponent can't cast X and plays with their hand revealed. {U}{B}, {T}: Put X into target opponent's hand. {3}{U}{B}: You may play a land or cast a spell from the hand X is in. If you cast a spell this way, you cast it without paying its mana cost.