The first time you encounter this boss, I would suggest dashboarding and creating a copied save. To dashboard, hit the Xbox guide button and quit to dashboard. Now, go to your hard drive memory. Find Prince Of Persia: The Forgotten Sands, and opt to copy it to another location (memory card or USB). Now play from hard drive. If you get hit, you can reload your checkpoint. There are two portions of this fight, so you will hit a checkpoint in the middle. Here is a video. During the cut scene, you will notice the boss hits me. I do not have Stone Armor active, but I still get the achievement. The cut scene hit does not count as taking damage.