So I was watching my brother play the Rise of Iron DLC for Destiny and I had an idea during the first boss battle. My thought is that, depending on the difficulty level, only a percentage of the boss’s health comes back. So if you are playing on normal then the boss only gets 25% of their health back. Of course this would change with the difficulty, so hard mode would get 50% while extra hard would get 75% or 100% back. I think this would a nice little wrinkle when creating boss fights.