Mandy hits a baseball with one of Grim's bones, yet when we see Grim, there are none of his bones missing from his body.
Nergal is the villain introduced in this episode. "Nergal" originally was the name of the Babylonian God of Fire and Guardian of the Underworld. In the Bible, he is one of the demons allied with Satan himself. In the series Nergal is associated with the underworld and fire.