This is basically an achievement for getting all the other achievements.
Here is your checklist for getting 100% completion. Obviously I set up this solution so as you complete the other achievements they will appear green in sections 1 - 3 below after they have been scanned by TA.
1. Complete the Riddler's and Amadeus Arkham's achievements.
2. Get 24 Predator and 24 Combat medals in Challenge Mode.
3. Complete the game on any difficulty. Since difficulty achievements stack you should have the achievement for easy no matter what unless your game glitched and didn't reward you.
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