City of Chains

When in the warehouse siege bit, you have to be uncaring and cold towards Rebecca. So any time you get a choice to express what you think about the situation, you have to choose the 'I don't care' options (or the equivalent), and when talking to Rebecca, tell her that on a second thought you've changed your mind. If you choose all of the right options, then later on, when you're on the way to your final mission of choice and you see a cutscene of Rebecca talking to her father, she will appear all emotionally troubled by what happened to her, and her father will say he'll get Sgt Burnett to help Roddrik in catching your team. Then, during the final boss fight, Sgt Burnett will be there to replace the flamethrower trooper and you get the achievement at the end of the fight. He is roughly the same level of threat as the flame trooper, and is simply more of a secret character that you find from one of the choice and consequence branches than a secret boss.

Additional note:

• When the psycho asks you what you think, DONT tell him he is sadistic, choose the other option. I personally like to choose to kill Olivia to be extra mean.

You don't retrieve the package and tell Leo the truth that you know about him.

He gets annoyed and says he'll get you for this. Later on, in the final hub area, which is the one after the warehouse siege part of the game, you get to meet him again.

To find him, if you go to the Southern part of the area, you'll see a building guarded by 2 robots.

Across the road from it, to the South, you'll see a small alleyway. Go down there and you'll find a chest to loot.

Take the contents of the chest, and at this point a cutscene will be triggered and Leo will reveal himself.

There's no battle or anything, just a cutscene. After that the achievement should be unlocked. 😃

Roddrik's wife must be killed for him to storm in and punch Jinn to death (either if you choose her to be shot or if you refuse to choose altogether and Jinn shoots both hostages anyway)