The Steel Mill Assembly Line
The next area through the door is the Assembly Line -- pause to listen to the conversation here, and then look back towards the door you just entered through and, on the right side, you will notice an odd statue... This is actually one of the collection items for the game (if you played the previous game you will recall the dancing teeth? This is pretty much the same thing but not dancing teeth). Do not worry about this or the other types for now because you don't have the gadget you need to destroy them...
When you approach the door Batman remarks that it is too well-covered and he needs to find an alternate route -- turn on Detective Vision and you will see a switch in the back corner on a conveyer belt that you can press to open a door and then duck and enter. Grapnel up and you can see perches inside to occupy -- IF they see you here, use a smoke pellet then get to a perch above quickly.
Getting Through the Assembly Line
Move to the perch on the far wall behind them, drop down silently and get behind the guy who is on his own and do a silent-takedown on him, then do a silent-double-takedown on the remaining pair, following with a Left-Stick Double-A tap to jump through the nearby window!
In this area you can grapnel up to the very top to find one of Catwoman's Trophies -- remember, YOU cannot take HERS, but she can take yours... So mark this on the map for now and then turn on Detective Mode and voila! There is in fact a Trophy for you to grab here! Demo the wall and pick up the Trophy and then drop back down to go through the doors into the Smelting Chamber area.
--== Smelting Chamber ==--
To the left of the doors to the Smelting Chamber is another of the Harley Dolls - you can walk over to it and press 'A' to hear different recorded messages if you like... When you are fully amused, head through the doors and pause to hear a nasty conversation, and then crouch. Batninja to the two armed thugs ahead and do a silent-double-takedown on them -- if you do it right none of the others will notice.
Now make your way through the room you just passed and out the other door, corner crouch by the top of the stairs and -- when it is safe to do so -- sneak down to the level below and drop under the grate there!
There is a patrolling thug who will walk right up to the end here so you can take him down from below, popping up. This will draw the attention of another thug, so just pop back down and wait for him to come and investigate and rinse-and-repeat on him! Go up to a perch to take the last outside thug down and then drop down to the catwalk and ninja to the grate near the room with the thug who has the doctor...
I was not able to get into the duct without getting seen -- but you might -- either way take out the last thug, then rescue the doctor to get a CS in which you learn about the Joker's "illness" -- yeah we know what Titan is, and this is bad news...
After the CS ends we get a new gadget for our efforts -- a Remote Electrical Charge -- which should prove useful! I say that because among other things, this will allow us to power up the different motors that we have been encountering in the other areas and thus will give access to Trophies and other areas, and it is the device we needed to start blowing up the Harley Dolls -- and how cool is that? Very cool!
So why not test it out on the one we just talked to Harley through? Yeah!
Rescuing the Doc
With that mischief managed there are a few other things to do here -- if you are collecting Trophies head through the duct we entered here by and grapnel up to the ledge above to pick up the Trophy here. Now when you exit the office the game will snap your attention to the inert motor across the room -- you use the REC on it to proceed -- but not just yet mind you. No, first look to the right and you will see another round hatch on the wall while in Detective Mode. That's right -- another Trophy is concealed there!
Use the Grapnel and then use it again to get the Trophy, and then head back to the office and through the double doors there to Cooling Tunnel D -- inside is a metal cart and against the back wall a motor -- use the REC on the motor to pull the metal cart to it then look under where it was to get another Trophy! On the wall here is another Harley Doll -- destroy that and then drop down to the ground in the main room -- across from the demo wall and a grate that leads back to the previous grate area is another Harley Doll -- so destroy that!
Ignore the grate and demo wall as you have already covered the area that they lead to... Now it is time to use the REC on the motor and exit this area. Inside is another motor and behind its grate, a set of doors -- use those and then Grapnel up the level above and go through the duct to end up behind the thugs who wielded the other door closed -- take them out now!
Assembly Line Part 2
After you take out the thugs go through the door and use the REC on the motor to draw the bumper cars to it, and then pull open the vent here, going inside to gain access to another Trophy -- you notice that these things are unlocking maps right? Yeah, they are!
Now backtrack to the bumper car room and enter the office on the opposite corner from where we entered, destroy the Harley Doll here, and then exit through the door beside it, then head through and out the next door for a brief CS with Harley!
There is another Harley Doll in the corner on the other side of this room so go destroy that, and then use the REC on the motor here two or three times so that it swings the hook into the office wall smashing the facade and door open.
Our First Mini-Boss Battle with Mr. Hammer
When you Grapnel up to it you end up getting knocked back by one of Harley's freaks -- Mr. Hammer -- and you suddenly find yourself in a mini-boss fight! You are shown how to use the REC to stun in combat -- LT 'B' -- and then the battle is on. Your best strategy here is to take out the regular thugs first so you only have to deal with Mr. Hammer on his own!
If you have any trouble with this battle just watch the video and do what I did -- it really is not a difficult fight at all! Completing it also unlocks the Achievement "One-Armed Bandit" (10GS) for defeating Mr. Hammer!
Now head up to the office above again and go inside for a CS with Harley and then... Well... You fell for one of the oldest tricks in the book...