There are new insane inmates in this area, however you should be more concerned about Ivy's plants. Each time you'll approach one of the plants it'll release glowing spheres. Your objective will be to destroy these objects using Batarangs before they hit you. I would recommend destroying the plants as well, however you'll earn only small amounts of experience points.
Start moving towards the Arkham Mansion building. The main entrance is going to be blocked by large roots, so as a result you'll have to find your way to the roof and from there to a small ventilation shaft. Walk through the tunnel and open a new door to travel to Mansion Entrance Hall area.