It's about time they added % remaining for your target.
Every coil boss uses % phases pretty much, but this was unacceptable in coil 7.
For those who don't know, moving past a certain % in 7 would move into the next phase. Acceptable, except that the bosses move rotation starts over, and the only way to avoid one of her abilities (a AoE petrify centered around one of your party members) was to hide behind petrified Renauds to create a save zone 'cone' your team stands within to avoid. The issue is if you pushed the boss into a phase incorrectly, the Renauds would wake up and kill everyone pretty much instantly.
This mechanic was strictly pushing the boss into a certain % after she used an ability. There was no way of knowing (legitly) of where her HP was at before pushing it.
This should have been in the game sooner, but I guess they added it because of what they did. It's easier to add a % than to fix your own content the players already had to learn.