A Necrodermis is the false body used to contain the compressed essenced of a C'tan when it manifests, thus allowing it perceive the material world. Each Necrodermis is made of the living metal originally developed by the ancient and long dead Necrontyr for use in their starships. The shape of a Necrodermis can be modified at will by its C'tan inhabitant, leading to vast differences between the bodies of each Star God. This also allows the spontaneous formation of cutting and slashing weapons as required.
If the Necrodermis is breached, the essence of the C'tan is released, accompanied by an explosion of some form, which can damage nearby units. This is but a minor setback for the C'tan however, as a new Necrodermis can be reforged and the C'tan can cross the incorporeal starlight bridge back to the material realm once again.