This achievement is story-related. You'll unlock it by completing all 4 chapters of the 4th act.
Other than keeping an open eye for all the different collectibles there isn't much to look out for in this act. Be aware of the
If you have problems at any point, please refer to the videos below:
(video credits: XCV //)
Hope this helps you guys!
Any improvements? Please let me know in the comments below!