Fun concept!
If I had to find something to complain about it would be how the flames dealing damage can make it so you only have to play the beginning of the exorcism and then move away from the keyboard until the boss is done.
As the flames stay there until you pass over with the mouse, you basically get a firewall that kills every single ghost.
What if the flames slowly crept towards the player? What if they despawned after a bit if not collected?
Had good fun playing it, though!