This is a really interesting concept, haven't come across anything like this before and I'm quite intrigued by the possibilities! I wonder if perhaps there something that one could do to make it a bit more dynamic, perhaps damaging the same enemy enough would cause it to enter a recovery state where it's invulnerable and disabled for a time, forcing you to turn your attention to other enemies as well as allowing you to temporarily disable particularly troublesome foes. Hmmm, lots of ways you could go with this, though one change that would be nice would be to have the healthbar show the current health rather than only changing when they are below half. Awesome idea, and solid execution! Great work!