If you are specifically looking for a "Supernatural" RPG or handbook rather than an art book, resources like the Supernatural RPG Corebook Mutants & Masterminds Supernatural Handbook provide character and rules guidance. Quick Posing Tips for Your Art
Intense movements, combat stances, and floating/levitating-style poses often seen in supernatural media. Where to Find Guides and PDFs Supernatural Pose Book Pdf
These books feature professional models in a variety of setups that are highly useful for supernatural art: Dynamic Angles: If you are specifically looking for a "Supernatural"