By the time you are reading this solution you have surely come across the completion percentage score that will pop up every time you cause mayhem or complete something. This score needs to be raised to 75% in order to get the achievement.
To do so I recommend you play the story first. There is no need to concentrate on this achievement at the beginning. Once you have completed the story you should be in the 50% area. This of course depends on how many villages you have taken over and missions completed. You will gain a certain percentage for doing the following:
- completing locations (about 0,03%)
- causing chaos adds (about) 0,005% per destroyed item
- killing colonels (about 0,14%)
- finding faction collectibles (about 0,03%)
- completing challenges (about 0,1%)
- collecting resource crates (about 0,01%)
After completing the story you will automatically switch to
Mercenary Mode where you can roam around Panau to get more completion score while keeping what you did in story mode. I recommend you concentrate on the following achievements first before going for the remaining percent.
A Trusted Ally in Just Cause 2Up to the Challenge 2 in Just Cause 2Trying Everything Once in Just Cause 2Faction Benefactor in Just Cause 2Leaving No Rock Unturned in Just Cause 2Freeroamer 2 in Just Cause 2Destroyer in Just Cause 2Professional Hitman in Just Cause 2While doing these I also recommend stopping now and then to do some unrelated tasks to mix things up! You should end up with a completion percentage around the 70% marker depending on how much exploring you did before. All that is left to do is clear bases and villages while rounding up collectibles. Try to focus on the big bases first. The big harbour in the middle of the inner sea hold a lot of destructible objects (and a challenge for which you pretty much have to take out the SAMs first). Airports are also a good choice as are big cities.
Here is an
interactive map that might help you get to the locations of interest. Many thanks to
ReptarOnIce3000 for providing the link!
Edit - 15 September '14: Updated map reference.
Edit - 3 February '17: Updated map reference as by comment.