So, watching Lab Zero stream God Hand, I caught a comment from Mike saying that, if he had a mode where he could play as the drummer guy in the band battle, he totally would.
This got me thinking (quick, run away while you still can!), all enemies have attacks with hit-boxes, sound effects, animations, etc, right? From a data end, there's little difference between an Incarnation and an enemy, except for AI, plot stuff, and platforming elements. So, from the back-end, it seems feasible to "recruit" any enemy for battle! Especially if enemy attacks already correspond to "down, neutral, up, special." Hungry Ghosts and Scribble Cat have already been put under the controller for walking-around testing purposes. Perhaps a second-playthrough "Snapshot" ability could allow the player to use enemies and bosses! It could be like Sketch or Beast Master from Final Fantasy.