Quicksilver Dragon is a rare Creature — Dragon card from Onslaught (ONS), collector number 103. Current market price: $0.78 (foil $19.84), TCGplayer market prices via Scryfall.
Flying {U}: If target spell has only one target and that target is this creature, change that spell's target to another creature. Morph {4}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)