Source: Breaking the Bones of Hell, pg(s). 88
Shadow golems are a particularly exotic and hard-to-create type of golem constructed from shadowstone. Its body can only be crafted on the Shadow Plane with special tools and anointed with the essence of usually unwilling natives of the Shadow Plane; because of this, shadow golems have been associated with evil despite not being evil entities themselves. The shadowstone, although tempered into a solid shape, retains its strange properties, allowing the shadow golem to walk on the air or to resist physical attacks. The typical shadow golem stands 11 feet tall and weighs 400 pounds.
On Golarion, shadow golems are most common in Nidal. Artisans in service to the Umbral Court jealously guard the secrets of creating one, only sharing them with a few others, including House Thrune of Cheliax.