To get this achievement you will need to get all most wanted missions done, That includes you getting all riddler trophies, I know fun right?
Once you have 8 most wanted prisoners you'll start the first part of this achievement, Then to unlock the achievement you have to get all 12, Along with getting all 12 you get the full ending to the game which is honestly insane.
Just a note: if Azrael attempts to kill Batman instead of breaking the sword, he would be taken to GCPD as well, making the max no. of most wanted criminals 12 instead of 11.Also if anyone is scared that after you do the knight fall protocol you go into a point of no return that's false. The game will just put you back at the bat signal after the cut sense.
EDIT: Don't forget about Death stroke, He comes after you do all the bombs and checkpoints and watchtowers. The guide for him can be found here if you're having any trouble.
If there is anything I am missing please let me know so I can add it, and if you vote neg please let me know to help improve my guide.
If you're having any trouble finding the green dudes throughout the world or stuck on a trophy check out the guide that I made here:
Credits: ImaginaryRuins for pointing out the max can change depending on if you made azrael attack batman or made him break his sword.