Batman: Arkham Asylum Guide - Walkthrough
As you enter you see a mini-CS in which Zsasz appears with a knife and backs into the inner office holding the Doc hostage and warning you to back off. Go ahead and turn on Detective Mode now so you have a better situational awareness for where the bad guy is and what he is doing.
You probably noticed the Trophy ahead and to the right – ignore it – you cannot get to it without being seen, and forget the zip point above as well, there is nothing you want up there right now – though there is a pair of Dancing Teeth so remember that for later.
A few things you need to know – if he sees you, he kills the Doc and you fail. If you wait too long, the timer you cannot see runs out, he kills the Doc and you fail. What you need to do is wait for him to back into the inner office and then run along the wall on the right until you reach the divider thing that is poking out. Now ease around that and crouch, and move towards the opening to the inner office until you get the wall hugging prompt, which you initiate.
Now elect your Batarang and go into target mode, target Zsasz' head and launch it FTW and the Achievement: 'Zsasz Cut Down to Size' (10 GP). You now get a CS in which the Doc goes a little ballistic on Zsasz and you stop her. Now you get a little more info on what is going on and then a surprise explosion and a CD of Harley doing her thing and a squad of henchmen you are going to have to deal with when you get back on your feet.
One of the thugs has a shock baton so do not attack him – quickly melee the three who do not, knocking them down, and then dodge (double-tap A) to the far side of the room and select your Batgrapple, then target the baton thug and jerk him towards you while you dodge aside, disarming him. Now you can take the four of them out as you like – either by pummeling them or doing takedowns.
Once they are down you get some nice XP, your health restored, and a new objective – take out the store of Venom in the Gardens. You also need to scan the Warden's Office for forensic trails so go ahead and switch into Detective Mode now to do that!
Scan the baton on the floor to obtain the Warden's DNA to track, and then walk forward and grab the Joker's Secret Map off of the desk here. As you follow the clues out of the Inner Office head to the right to grab the Riddler Trophy and unlock a new challenge, then go to the next clue towards the exit and pause – remember the Teeth above? Go ahead and zip up there and kill them for the bonus XP and to add them to your Teeth kills for this zone.
Exit the Office to the East Wing Corridor and move along to the corner where you will encounter another box of three Dancing Teeth – and kill them. Now exit into the Main Hall and move forward and to the right around the structure here. Behind it is a grate – rip it off of the wall and enter the structure to find the third patient interview tape for The Scarecrow. Give that a listen and then notice that you picked up the bio for Catwoman at some point in this section – good on ya! When you exit back to the game you should now receive the Achievement: 'Lateral Thinker' (20 GP)!
There are three armed thugs in the room beyond the exit – but there are also Gargoyles ringing that room above, so hit a Gargoyle and work your way to the far side of the room, where you can drop down and silently kill the first two thugs. I am not sure if this always happens, but for me, when I took out the second thug the last one noticed that something was wrong and ran back to the body of the first thug to investigate, at which point I zipped up to the Gargoyle above to avoid detection. When the thug moved back into the open I did a glide kick and ground takedown FTW.
As I headed for the door nearby I got my next upgrade – choosing the Multiple Frequency Detonator.
Exit into the Mansion Entrance Hall and you will be taunted by Harley – and notice that the security forcefield is no longer active on the main door. Follow the clues to the door and exit the Mansion now.