Add some kind of object in the background to denote where checkpoints are. I had died in the optional area in the Usher Bot stage and got sent back a lot further than I thought I would (had to go through that long climb and roof segment again). The boss itself was really challenging. I wasn't able to beat it. I'm not very good at these games though. Maybe reduce the amount of time the holy water is active?
I'm looking forward to seeing where this goes. The dialogue at the start of the level is funny and campy.