Lego Batman Strategy Guide 70: Batboat Battle, Free Play
After the first area, when you blow up the gate, there will be two red lights. Transform into Penguin’s submarine and go underneath them, and aim for the bricks underneath the red lights. This will cause a crane to drop down two red and green things, which the Robin Cycle can target with its missiles. When these two things are hit, a ship reminiscent of the Titanic will appear. Sink that ship with two missiles, and it will go down just like the classic White Star Line. It will leave behind a floating ring, so shoot that in order to get the Sixth Canister.
Eventually, you will get to an area where you will see a canister floating in the midst of what looks like a hole in the ice. You were never able to get there the first time, but now you can become the Penguin’s submarine and go under the ice. Surface, and you should have the Seventh Canister.
You will notice a silver area that is floating in the midst of toxic waste. You can, as the bat boat, can a mine, and drag it toward the toxic waster. Release, and it will hit the silver thing, which will explode into a canister. Be sure you become Croc’s boat, as that is the only way to get the Eighth Canister.
In the final area, with the giant-sized submarine, you will find that there is a pink window on the right. If you remember from when you played as Penguin’s submarine, this is where you can get some torpedoes. It is a must for taking out the pink and white gate by the submarine.
Go through this gate, and you will find a nice surprise in the upper right corner. You will need to submerge as a submarine, and when you Surface, you should have the Ninth Canister.
Now, there is a way to get even more right than this. Just become a submarine and submerge to get to this area, and you will be in an area where four targets are in a perpetual state of rising and falling. Once all four targets are shot down, you will have the Power Brick.
Now, there is another area to the left that is full of toxic waste. It has three silver platforms floating in it. You will need to turn into the batboat and then go back to where the giant submarine is to take it out. What you need to do is get a mine, and then somehow get it to drift there. Even though there are three targets, it should go down with one hit. You will then have the Tenth Canister, and you can become Killer Croc’s boat in order to retrieve it.