If you are having trouble on getting this achievement, there is a creature core that is gonna be your lifesaver. The core is "Legion Shieldbearer". This is the boss of Chapter 14, but you can farm him in the arena. Basically, this shield is gonna make you invincible for at least one hit every time, so if he hits you twice then he is gonna cause you some damage. The point here is to avoid at least an extra hit, which is very useful in some situations. The achievement asks you for no damage, so he can hit you as long as he doesnt hurt you. Give it a try for practice to see how it works.
On the other hand, there are some critical moments which you must be careful, like when his health is low he will start creating a lot of crystals around the map. Use the special attack of Strife (
), as commented in another user tips, so you wont get hurt as this attack makes you invincible, but be aware to dodge when it ends. Also, the moment you can use the Anarchy form
(usually almost at the end) dont hesitate and use it, to make sure you dont get damage in the last moment.
**These tips are considered for the easiest difficulty**
- Image of the core: