I tried to make their purpose evident through playing. There is a life bar on the far left, and two track lists. One track list shows the currently playing tracks, red, purple, and/or blue. And the second one shows the queued up tracks. When a music box is killed a little particle moves the track into the queued tracks. When the current sections is complete the queued tracks become the playing tracks.
The tracks being played also correspond to the backgrounds being displayed.
I had thought about limiting the shooting, but decided against because I didn't want it to become frustrating.
Thank you for playing.