Intensive Treatment--Part 2

After dropping from the vent, proceed to the cop ahead, who's looking into a room filled with toxic gas. Look up when instructed to find a grapple point at the top of the vent directly above. Climb up, then bust into the nearby vent and out the other side.

Rescue the guard clinging to the ledge, then jump the gap (simply by running toward it) to the next platform. Now grapple to a ledge above, just ahead, then glide to the far platform below (again, simply run off the platform toward it).

Upon landing, rescue the convict hanging from the ledge, then activate detective mode and look in the control room below to spot a control panel on the wall. Toss a Batarang at it to activate the fans, clearing the room of the toxic gas. Drop to the floor below and proceed through the door, just right of the control room, and follow the arrows on the floor to a far door, where a boss fight awaits.

Alright, so the key to taking this guy down is…to do nothing at all! Seriously, just stay as far away as you can and use the evade move to dodge his attacks. After about a minute, he'll fall over dead. If only the rest of the game's bosses were so easy…With the boss defeated, talk to the guard inside the small control room to the left.