The best thing you can do is go on the left, and rescue Hostage 9/25 is on the left side here.

On this right side is also a ladder that you can build, and it will take you to the top where the First Canister is. You will need to activate a dual pressure pad to get it.

Go to the center and destroy some stuff by the glowing area to get a Demolition Suit. Go to the right, and grab a railing to a platform, and haul Batman up to destroy a silver gate. Send in Robin to get the Suit Upgrade of a Magnet Suit. There is a gargoyle up there that can be blown up that is 1/3, and one in left corner is 2/3. Yes, these are required to get a canister, but you won’t be able to get it until later. I actually believe you can get another way, but I think I shall save that for Free Play.

On the tower on the left, there is a pillar you can destroy. You can use the wreckage to build up a magnet area for Robin to go up. Let him keep going to the right and spin a spinner.

This will stop the bad guys shooting at the front, and free up Harley Quinn. Take out whatever men are left by the entrance, and go to the gun/trucks. Hop in and shoot her with the bubble rays. When you hit her, she will throw something explosive. The trick is to make certain you have jumped out before it hits. Shoot her with the other one, and she will destroy it too. Fortunately, you can build a final gun with the remains of the wreckage and take her out.

A gargoyle statue will drop, and you can build a fan from out of its wreckage. Let the fan take you to the top, and you will be in another place.

Here it is a matter of chasing Harley. If you go right, you will come to an area where you need to build a lever. Pull it, and something will go down that will bridge to the other side. Keep going until you get to the top of a spiral stairwell.

Build some magnet tiles, and have Robin walk up and through a small hall until he can pull a lever. The Second Canister will be on his right.