Just out of curiousity - how would you stat up a skin walker? Specifically, an old and powerful one?
I'm thinking supernatural toughness (or better) and or regenerative powers. Also, true shape shifting. I'm unsure of whether to stick to Navajo lore and keep them being powerfully perverted humans, or just make it a supernatural creature. Or perhaps both: it's a demon who possesses humans and - while in this form - grants the body shape shifting powers.