If you're really having problems with this boss: 1. I recommend using red candy and fire to quickly kill the second ape because it's the main pain-phase. 2. Then just keep distance if you can and wait for her longest combo and parry the last attack, get a good load of health and repeat. 3. After about half of its health you can parry a kick or two and keep distance when you don't feel like it
. Continue until its posture is broken. Headless itself is surprisingly more scary than hard and by that time you should be pretty familiar with his moveset, so don't be afraid to loose most of the flask on the second ape phase.