Necrodermis
(Rule)Description: C'tan have a Invulnerable save of 4+. If it loses all of its wounds, the nexrodermis is breached and the essence of the C'tan is released. This inflicts a S6 hit on every model within D6" of the C'tan with no Armor Save possible.
If a Wraithcannon inflicts instant death on a C'tan it will not be transported to the warp but will take a wound without the benefit of its Invulnerable Saving throw. If a C'tan phase sword or knife strikes a C'tan it will inflict no wounds.