Batman: Arkham Knight

Spoiler Alert:

This IS a main storyline achievement. Immediately after you have fought the Arkham Knight in the tunnels you will then find yourself underneath some grates below Commissioner Gordon who is getting the crap beaten out of him. Line up your attack (I suggest a FEAR takedown) and dispose of all the guards in the room. When you go to release the Commissioner you will be confronted by the Arkham Knight who finally reveals his identity. Now you will have to fight him again, don't worry too much this part isn't too bad.

The fight is broken up into several segments with the formula (predator room with Arkham Knight followed by a room filling with Gas, rinse and repeat).
In each of the predator rooms the Arkham Knight will be seated atop a ledge with a sniper (the red sights coming from it indicate where he is looking). The first thing you should do is disable (remote hacking device) the flying drone, then dispatch with each of the guards, Once it is just you and the Arkham Knight sneak up to him (avoiding his sights) until you are directly below him, then grapple up. (In the final predator room, the one with the turrets, just take your time and time your runs, also disable the flying drone again).

The gas rooms are real simple, once you get control of batman (just after he has tangled with the Arkham Knight) simply grapple to the right statue, then grapple to the vent on the shutter wall (Hold RB).

After the fight with the Arkham Knight there will be some dialogue. Rescue Gordon and head to the elevator. When it opens up there will be another fight but just with some simple guards and an electrified brute (quick charge). Take the elevator up with Gordon and listen to some pretty sweet dialogue. Once the whole cutscene is finished you will be tasked with protecting someone and lucky you, of course batman has a spare batmobile (didn't see that coming *cough*). Destroy the tanks, place the person in the batmobile and BAM the achievement is yours.