In their "natural" form (so to speak), Skinwalkers resemble skeletons, whose ribcages are filled with twisted, discolored and distorted mockeries of normal organs. 

Skinwalkers kill and skin their victims, eat their brains and wear their skin, and masquerade as them. Their consumption of the brain gives them access to their victim's memories, and allow them to mimic the victim nearly perfectly. Their twisted organs can  preserve the dead flesh for weeks, months, even years if they are careful, or capable of otherwise magically preserving the skin before it begins to rot and they must move on to a new victim. 

The Blessed