The Ur-Sphinx is a rare Legendary Creature — Sphinx Avatar card from Reality Fracture Commander (FRC), collector number 12. Current market price: $1.37, TCGplayer market prices via Scryfall.
Eminence — As long as The Ur-Sphinx is in the command zone or on the battlefield, other Sphinx spells you cast cost {1} less to cast. Flying Whenever one or more Sphinxes you control attack, each player mills that many cards. For each player, you may cast a card that player milled this way without paying its mana cost.