I had a different vision of what you described
Ok close your eyes and listen... now would world battle fit in there? no, not really, but in my opinion no. Boss battle, hmmm, yes? Secret boss battle would be the answer. This is pretty epic, now with my eyes closed I see a Puppet or Puppet Master facing the main character, (this would catch a player by surprise as for the song im sure has caught people by surprise) as the Boss comes closer to death, he begins to control more puppets to increase the difficulty. Overall: very Unique - I can see this being used in an action rpg game. although there were little dull parts in this but still the best non the less.