The Shadowstone is an important item in Spyro: Shadow Legacy that allows Spyro to switch between the real world and the Shadow Realm. It is a powerful Elder's amulet that sharpens and focuses Spyro's magic. It also helps Spyro find any people trapped within the Shadow Realm.
According to Tomas, the Shadowstones usually knock apprentices out cold, but Spyro has a natural ability to withstand its effects due to his powerful magical energy.