Rattleclaw Mystic is a rare Creature — Human Shaman card from Khans of Tarkir Promos (PKTK), collector number 144s. Current market price: — (foil $2.33), TCGplayer market prices via Scryfall.
{T}: Add {G}, {U}, or {R}. Morph {2} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.) When this creature is turned face up, add {G}{U}{R}.