I knew I wouldn't have enough time to make a compo entry, but I am quite pleased with my progress for the jam. I have a much clearer idea of how the game is going to play, and I caved on not drawing any graphics, so I have a screenshot (this sadly doesn't show the multiple levels of parallax I have going!):

The game is going to basically be a Paperboy clone, with Charon speeding down an infinite river Styx, picking up souls every so often and flinging them into the correct parts of the Underworld on the opposite bank. The targets will be reasonably tricky to hit, and there will be obstacles in the river to avoid. I think that will make it fun. Anyway, time for bed!