Scion of the Ur-Dragon is a rare Legendary Creature — Dragon Avatar card from Secret Lair Drop (SLD), collector number 1531. Current market price: — (foil $21.90), TCGplayer market prices via Scryfall.
Flying {2}: Search your library for a Dragon permanent card and put it into your graveyard. If you do, Scion of the Ur-Dragon becomes a copy of that card until end of turn. Then shuffle.