Maybe you could trace over the player sprite and make it look like the main character when he was alive. I could recolor it as blue on my end and increase the opacity, and boom, a ghost/spirit!
Looks great. About the multiple layers and bosses. We might have just enough barely time for one more of each. But I think we should polish some and add smaller stuff for now instead of making the game buggy with unfinished content when it gets released.
I can try to release it early tomorrow so you can try it out.