Sweet game, it was a bit frustrating at times but I enjoyed the challenge. The movement and shooting mechanics are done well and sacrificing lives to get forward is an interesting mechanic.
Some tips: I got stuck on corners sometimes when I was moving forward and jumping. I think it should cancel my x velocity if I collide with something from the side. I also found the alpha num 1 key weird for switching and would have preferred Q or R. It also took me a bit to figure out something was destructible so I think it should be colored brown or something instead of gray. Lastly, it was sometimes difficult to figure out when I would need to worry about getting shot, so some invincibility frames when I stop being a ghost would be nice, as well as a visual timer.