They are malevolent shapeshifters who feed on souls.
The Yaoguai are China’s demons, lurking about and feeding on human essence. They are usually evil animal spirits or fallen celestial beings, seeking immortality – and they need your soul to get it! They’ve been known to appear as foxes, skeletons, and even beautiful seductresses in their search for prey. They especially like to abduct and consume holy men, though they probably wouldn’t turn down a lesser snack…
Image found at http://horrorhk.blogspot.com/2009/08/blog-post_6543.html