Return to the Sewer--Part 1

Inside the cave, glide to the strip of land below, then grapple into a high vent. Continue through the Old Sewer into the Main Sewer Junction. Proceed through here, much like you did near the start of the game. Once you reach the top, use the Line Launcher to cross the gap to the central structure, then climb up a couple ledges to the right, where the Oracle will radio in with your next objective.

Secure the Pump Control Room

Cross over to the far side of the structure, then turn around to face where you just came from and use the Line Launcher to reach a high ledge. Continue climbing up this section as high as you can, then turn around at the highest point to spot a weak wall that can be pulled down with the Ultra Batclaw. As soon as you do, three enemies will approach the ledge from within; fire the Batclaw at them too to pull them into the abyss before grappling inside. Inside, kill the last remain enemy then grab the Secrets map from the chair before proceeding through the hall (look for an Interview Tape just before the door). When at the Pressure Control Junction, you'll reach a split path--the left one leads to the West Pump room, the right leads to the East. You can tackle them in either order, but for the purpose of the walkthrough, we suggesting heading left first.

Shut Down West Pump Room

Upon entering the West Pump Room, you'll find several guards below, one of whom is armed. We suggest using the Ultra Batclaw on a group of three (including the one armed!) to briefly stun them. Then quickly drop down, cape stun the group, then ground-takedown some of the initial three. Once you've cleared the room, use the Sequencer on two control boxes on the wall to shut down the west room. Now head for the East one.

Shut Down East Pump Room

The East Pump Room is a bit more difficult, as all of the enemies are armed. Thankfully, we found a nearly fool-proof way to easily take these guys down. First, sneak up on the guard down nearest to the hall for a Stealth Takedown. Of course, this will tip off the rest of the enemies to your presence, so duck back into the hall, using the jutting corner closest to the door for cover. Now here's the trick: as soon as the enemies start trickling in, use the Ultra Batclaw on them to pull them to the ground, stunning them. Repeat this as more of the enemies storm in until most of them are on the ground, allowing you to begin perform ground-takedowns. Just keep an eye out for enemies getting back up and promptly Batclaw them back to the ground. With the room cleared, enter the control room on the right and use the Sequencer on the control panel within to shut down the Pump Room.

Stop Poison Ivy From Polluting the Island

As you return to the Pressure Control Junction, one of the roided-up baddies will attack, and he'll soon be joined by multiple waves of crazed inmates. Basically, you should battle him like before: that is, throw a Batarang when he charges and then attack him after he collides with a wall. Or even better, lure him into one of the electric gates during his charge to inflict even more damage. Eventually, you'll be able to catch a ride on him and storm around the room laying waste to the inmates--it's generally best to circle the room, allowing you to more easily control your ride. As for the inmates…well, they can be tricky. It's generally best to stay on the move and let the roided-up guy take them down for you. You can assist in the process by luring the big guy through the group during his charge, bowling them all over, giving you a prime chance for some Ground Takedowns. When he punches the ground is another great chance to takedown the inmates, as they'll all collapse to the ground. Those aside, keep your Ultra Batclaw equipped to easily stun three inmates at a time if they get too close for comfort, and keep catching a ride on the main baddie's back to take down more inmates. After the battle, enter the hole the big dude created and use the Ultra Batclaw to rip off a weak wall overhead. Grapple inside, scan the Chronicle within, then rip down a second wall further up. After grappling up, jump to to the nearby platform and plant some explosives, then jump back into the tunnel, where you can safely detonate them. With the rest of the shaft now exposed, pull down a third wall above and grapple up too. Blow your way through the dead-end to reemerge in Arkham West. Now use your map to head through the Cave System to the south to Arkham East. Once there, take down the snipers in their towers before attempting to enter the Botanical Gardens.