Batman Arkham City

This is an unmissable story related achievement. The last you will receive in the game.

The final confrontation begins with you in the open-world Arkham City and you have to dispatch snipers (7 if I remember correctly, plus 2 directly outside the door of the theater which you are trying to get into.)

The boss battle is a relatively easy one. There are 3 stages, the first 2 are about the same except said boss introduces some new attacks. The third stage small-scale enemies will spawn but they are easily dispatched.

The means of beating said boss are using RT -> RT to quickly lob Freeze Grenades at the boss. Do this enough times and run up and you'll be prompted to do a sword attack. The third stage occurs where you met up with Talia and Ra's Al Ghul earlier in the game (Wonder Tower underground.) You will actually be equipped with the sword for this part of the fight making the smaller enemies far easier. The same strategy applies for the boss in this round though. Double-tap RT until you're prompted to finish with the sword.

A few cinematics before and after said fight and alot of plot twists and turns, I hopefully avoided all possible spoilers.

If you're low on health by the third portion of the fight (and especially if you're playing New Game Plus), there's a fairly simple (albeit cheap) way to survive the mannequins: don't attack. Counter moves are instant-kill against those things, so while he's recuperating, just stand in one place and spam the counter button. When he pops up, immediately begin evading; don't hit RT-RT until RIGHT AFTER he's lobbed an attack at you.