Difficultly can be completed on: Easy
Goal: Don't get health to grey/less then one bar during the final boss fight.
At the end of the episode you will encounter a boss fight with "Barry". I found this achievement was very easy if you stockpile the flares for the boss fight.
There will be an ammo crate for revolver ammo and I believe also a shotgun crate. The first part of the fight consists of a few taken.
After the taken are killed, Barry will jump down get close to him, throw down flares next to him and shine your light to remove his darkness shield quickly and then unload into him. This will need to be done three times. Run up to him as quickly as you can and repeat with the flares and flashlight.
During the fight you will get swooped by multiple groups of ravens. If you are constant with flares they shouldn't do too much damage. You can tell the a group of ravens about to attack as they will screech right before doing so.
Once Barry is dead your achievement should pop.
* Note: Not I am not sure if checking point during the fight will still count for the achievement.