Return to Arkham Mansion--Part 1

Talk to Aaron Cash in the Arkham Mansion

After meeting with Poison Ivy, you'll want to work your way back to the Arkham Mansion, using your map. But first, as you exit the room, a large group of baddies will be waiting for you across the chasm. Before Line Launching across, use the Batclaw to safely pull most of them into the abyss, leaving just a few stragglers for you to deal with upon crossing. Now enter the vent in the southwest corner and use your map to proceed through the Flooded Chamber, to the Botanical's exit. As you close in, Poison Ivy will block it off--simply drop through the exposed hole, scan the Chronicle, and follow the path to a grapple point, allowing you to exit the place proper.

Back outside, proceed onward to Arkham Mansion--remember to enter it via the vent above the entrance. Oh, and try to avoid the plants along the way, as they can and will attack.

Once inside the mansion, you'll find it's been filled with poisonous gas, so you'll want to avoid the ground-floor. Instead, use the Line Launcher to cross to the other side and enter a vent above, which leads into the next room. To cross this room, drop onto the walkway to the right and follow it as far as you can, then Line Launch to the walkway on the other side. Now follow that path as far as you can, then Line Launch to the far wall and speak with Aaron Cash.

Gain Access to Killer Croc's Lair Via Intensive Treatment

After speaking to Aaron, exit the way you came in by grappling back to the walkway and then into the vents until you're back outside. Now use your map to head for Intensive Treatment. Although taking the Arkham East tunnel to the northwest is faster, it's also heavily guarded. It's easier to take the Abandoned Tunnel to the southwest into Arkham West, then through the Arkham West into to the north, leading to Intensive Treatment.