Each of three stages has random enemy mages, and played tracks depend on which mages are there (using a simple color checking).
Canceling the active fusion doesn't work (I didn't have time, even though I coded like frenzy ~17hrs per day).
But all fusions do work, so please check them all out, and also check the tracks, by replaying! :D
Here's a link to the game soundtrack, if you like some themes:
The art guy: