When you get up to the area where you can lean on the shelf to make stuff come down, you will see a canister on the left that you weren’t able to get to before . There are some tanks that you need to plant a bomb for, and you can use the wreckage to build a fan. Jump on the fan and you will be able to grab the Second Canister.

Keep going until you get to the one room with all the toxic waste on the floor. There is a shock generator there, and if you become the Joker, you can use his shocker to drop down a ladder. Climb the ladder, and you will come to a place where there is a railing. Become a high jumper to get to the railing, and go in and claim the Third Canister.

There is some junk here that you can collect, too.

Now, there is one more thing to do here. You need to go right, where there is a Question Mark window. Become a mind control character and gain access. In this room, there is a lot to blow up with explosives. On the left is something that can be destroyed, and rebuilt. On the right is something similar, but the parts that you can assemble are red hot, so you need to become Heat Protection Batman to build with it. Once assembled, push this thing in place on the right side. This will begin a machine that will eventually explode, and the reward will be the Fourth Canister.

When you get past the big garage door, you can finally get to the one area where the guys are shooting at you. Just go to the left corner and blow up some silver tanks, and then you can build a ladder up to the catwalks above. Climb up the ladder, and you can take out the shooters. If you follow it, you can even get a purple stud.

Go ahead and shift into Technology suit Robin and go to the control panel. You can use this little arm to grab some bombs on the upper left corner to destroy three pink smoking things. The gate will automatically open, and you can use the wreckage of the pink smoking things to build a dual pressure pad. Go ahead and put both characters on them, and the gate will open to get the Fifth Canister.