Objective 1: Follow Killer Croc
While Killer Croc may find these digs hospitable, the Boy Wonder certainly doesn’t—and who could blame him? Make this trek underground a quick one and start by smashing the green boxes just above where you dropped into the sewers. Then, use the fallen bricks left behind to fashion yourself a handy little grapple handle that can be used to reach the ledge above you. Once on the ledge, glide over to the right, following the trail of floating studs. Take advantage of the other grapple handle above you to access yet another ledge. On this ledge, you find a handy valve against the back wall. Give the wheel a few turns to drain the water from the area below you.
Now that the water has been drained, pick up the Token that appears nearby to outfit Robin with the Hazard Suit. Next, smash all of the containers in the area to reveal a myriad of Attract pieces (36 in all). Once you’ve collected all of the Attract pieces, deposit them into the Attract Station in the upper right corner of the area. Doing so causes a small red cannon to appear nearby. Simply stand behind it and grapple the handle on it to blast through the fence barring your way forward.
Unlocked: Hazard Suit
Another Token appears where the fence once stood. Grab this one and Batman is able to don his Sensor Suit, which will be useful very soon. Before heading over to examine the nearby green LEGO wall, drop down into the currently empty holding area to the right and smash the Batman prop in the far right corner. With the prop thoroughly smashed, use the ladder to climb back up to the green LEGO wall and peer through it using Batman’s Sensor Suit vision. While Batman peers through the wall, switch to Robin and take hold of the nearby valve and give it a twist until the rods within the wall align and lock into place.
This floods the empty holding area, allowing the wooden pallets within to float to the surface. Use them to clear the pool you just made.
Unlocked: Sensor Suit
Batman Smash Challenge: 1 / 2
Continue onward and you soon encounter Killer Croc. As he makes his escape, Killer Croc rips apart a pump assembly, contaminating the walkway and the water below with nasty, neon green toxic goo. Lucky for you, Robin’s Hazard Suit means that he is more than equipped to pursue the villain. Before you follow the reptilian menace, prepare to engage some of Croc’s Goons.
Objective 2: Find a Safe Path
Once the baddies have been dealt with, walk through the toxic goo and make your way to a platform which is being overlooked by Killer Croc and his lackeys (who Croc is more than willing to volunteer to fight you in his place). After you’ve dealt with the wannabe crocodiles, don’t forget to smash the nearby Joker prop. Once you’ve smashed the prop, use the grapple hook in the upper left corner of the platform to reach an elevator that can take you to the catwalk above.
The Joker Smash Challenge: 2 / 3
Follow the walkway, taking out Croc’s Goons in the process. At the end of the walkway, you find two blue pads that control the flow of the steam jets below you, as well as a Batman prop. Smash the Batman prop first, so you don’t forget it. With that out of the way, drop down from the ledge to the right of the blue pads (look for the grapple handle). Once on the level below, smash the nearby Joker prop and then use your grapple to climb back onto the catwalk.
Now, depress the blue pad on the left first, then switch to Batman and pass the now steamless pipe. Stand between the two pipes and switch back to Robin; this time stand atop the right blue pad to shut off the steam below it. Switch to Batman again and grapple up to the catwalk.
Batman Smash Challenge: 2 / 2
The Joker Smash Challenge: 3 / 3
Now that the Dynamic Duo is reunited, follow the path of the catwalk back to Killer Croc. Drop down to the floor below and use the Detective Mode of Batman’s Sensor Suit to reveal a grapple handle on the gold LEGO pillar that is supporting Killer Croc’s subway car. Pull on the grapple handle to send the track crashing down. Use the rubble to construct a ramp and enter the car to end the level.