Batman: Arkham City - Armory

You will enter a new Stalker area. Hop up to the statues and make your way over to Mr. Freeze's suit. Drop down and do a silent takedown of him. From this point on, they will scatter a little so it's a matter of separating them out and picking them off. I highly recommend hanging by the stairs because it seems to be out of view of almost every area (including the bridge). You do have to be careful to listen for them saying something about "So you think you can hide in the darkness?" which means they are going to use their infrared goggles to search whichever vantage they are near. If you are near him, move to a different vantage and you'll be fine. The only other thing to watch for is when you get rid of half of the men, one of them will take a hostage. From that point on, you can't be seen or you lose. Listen for Batman to give cues as to what not to do. For instance, I dropped an inverted body by cutting the rope with a baterang and he mentioned that if I used another baterang, they'd discover my location. Once you've gotten the last two guys, go over to a vantage by the bridge and wait for the hostage taker to turn his back. Drop down and sneak up for a takedown. Be sure to be fast. Head back to the Torture Chamber. Go to the Iceberg Lounge. On the way, there will be a surprise. You want to mash the strike attack and then continue to the lounge.