Stalking Stones is a uncommon Land card from Duel Decks: Elspeth vs. Tezzeret (DDF), collector number 75. Current market price: $0.17, TCGplayer market prices via Scryfall.
{T}: Add {C}. {6}: This land becomes a 3/3 Elemental artifact creature that's still a land. (This effect lasts indefinitely.)