When you reach the hallway with two hostiles and a place a ventilation shaft to climb up to, you'll have to secure the room to continue. You'll find out from the guard behind the glass that the next room is filled with gas that you'll have to clear if you want to free them.
Grapple up to the top of the ventilation shaft and break through the grate on the wall. Head through and you'll reach the top of the gas filled room. Walk around to the right, where the grate wall is. Use a batarang and aim it to strike the switch box near the floor on the far corner of the room. If you fall into gas, press Right Bumper once to escape.
Their radio went dead after you brought Joker in.
Riddler Challenge: defeat 5 Joker Teeth.
Cinematic: Batman finds the doctor who tells Batman it's a trap. Five hostiles jump down behind him and start fighting. Two of them will start by ripping heavy objects off the wall in an attempt to throw them, so fight your way to one side and then the other before they can toss them at you.
"Don't get too full of yourself bats, I'm just softening you up for the main event. You'll see."
Objective Complete: Locate and rescue Dr. Chen.
Riddler Challenge complete: Find a Riddle Trophy.
Place explosive gel on both doors, one behind two inmates, and one behind the solo inmate. If you only blow up one, the inmates will panic and shoot Dr. Young.
Objective Complete: Locate and rescue Dr. Young.
Cinematic with Dr. Young. She says they are hunting the other doctors, and
New objective: return to the doctors in the Sanitorium and pick up Gordon's...
First high security henchmen carry knives.
Sanitorium, cinematic. Dr. Young wants to get her research notes, her life's work. An alarm goes off.
You'll shoot up to the top of a gargoyle head as henchmen enter through the door. Pick them off one by one like you did when you first entered. This is a great time to use inverted takedown as the henchmen enter some of the small rooms (if you had blown up the hole in the ceiling of one of them, you can pick one off through it).
Enter the elevator and watch Joker's video on the screen. The elevator begins to lower, and Batman begins choking on gas. As he exits, a cinematic plays showing some doctors trapped in a room with the nerve gas.
Turn left and blow up the wall by the laser barricaded door. Head down the passageway past the Tobacco. Drop down and you'll see the commissioner being dragged, asking Batman to help. Open the grate in the corner of the room and go through the tunnel. You'll find the commissioner laying against a wall. Batman will take his pulse and you'll notice his eyes glowing. Batman is now hallucinating.
New Objective: hunt down the commissioner's killer.
Head through the door into the Morgue.
When you enter, turn around and head back through the door. Walk into the center of the new room and open the three body bags containing Batman's parents and Scarecrow.
When Batman awakes, you'll be in a new room. Hop across the ledges until you reach the cinematic with the Batsignal and a giant Scarecrow. You're in his world now. "Hide from Scarecrow's gaze to avoid being caught."
Start by walking around the corner and waiting for Scarecrow to turn past. Then run and jump across the gap. Climb up the pillar and head around the platforms. Hide behind the pillar, then spray explosive gel on the wall. Blow it up, then wait for Scarecrow to look around. When he looks around to the left, run and jump to the right. Hide behind the platform before climbing up, and wait for Scarecrow to spin around past it. Climb up and use the Bat Signal to kill him.
- Back to Reality
Head back out of the Morgue. Walk around until you find the painted arrows on the ground. Follow them until you reach the three enemies. You'll probably have to stun the high security henchmen to take them out.
Harley Quinn will be guarding the real commissioner at gunpoint. Open the grate to the right and head through.
Drop down from the vent, and take out the guard from behind. There's a Riddler trophy in a vent to the right of the first guard, and if you crawl out from the opening you can take another guard out. Two more guards are patrolling, and you'll come across two more in a hallway up ahead. Always use the vents to your stealthy advantage.
When the room is clear, climb up the stairway underneath the room where the commissioner and Harley are. Grapple up above the forcefield door. Grab the Riddler Trophy, stand on top of the glass ceiling, and press to perform a takedown. +
Batman will smash down through the glass and save the commissioner in a cinematic. After some chatting, Batman and the commissioner will stumble upon Bane's prison. Joker will pump him full of venom and he will break free of his jail.
Bane will push Batman and himself through the wall, landing in a place that looks like an Arena. Time for the Big Fight.
To fight Bane...
Wait for him to stop charging, then attack him. You can dodge all of his attacks, including the ground shockwave and when he throws chunks of the wall, by rolling. When the six henchmen come, keep your distance from Bane and take each of them out. Watch Bane's attacks and dodge them. You'll notice that the henchmen can be easily killed by Bane.
When Bane charges you, Quick Throw a Batarang (by tapping ) and dodge. This will cause him to not see where he is running and ram his head into the wall. While he's recovering, attack him with your fists so that his health drops. You'll notice Bane has three segments in his Health Bar. Keep up this Quick Throw, Dodge, Triple Punches until one of the segments is empty, and a short cutscene will play. Batman will jump on top of his back and pull out one of Bane's Venom tubes. Repeat this twice more so Bane is deprived completely of his Venom.
Cinematic: Batman exits the Building and taps something on his Glove. Commissioner Gordon comes to meet up with him, just as Bane breaks out through the wall behind them and grabs Batman. As Bane grips Batman, declaring he's going to break him, Batman says, "No Bane. This time, I break you." and Kicks Bane, releasing himself. Bane staggers back and finds himself suddenly illuminated by headlights. The Batmobile, which Batman had just summoned, rams into him, throwing him into the bay and finishing the fight. Batman then sends Commissioner Gordon on a boat back to Gotham, to take care of Joker's supposedly placed bombs there.