In the book, Riley Shiner encounters it when he's in a daydream, in which enters Shudder Mansion. The Dancing Skeleton starts dancing a sailor's jig, and Riley watches him for so long. The skeleton attacks him, and starts trampling him. Riley wakes up, and then, to his horror, finds two bony fingers gripped tightly in his palm.
It looks like a normal human skeleton, with a toothless grin and eyeless skull. It has thick spider-webs clinging to its rib-cage.