Down to Earth
From LEGO Batman Wiki
Part 1 is the fight to get onto the robot. Superman and Batman are behind the robot, Superman flying himself and Batman flying a helicopter that he stole from LexCorp Industries. First, you must use Batman to shoot the shiny metal LEGO bricks on the back of the robots feet. After this is complete, Superman must use his Heatray to destroy the shiny golden LEGO bricks on the back of the feet. Once complete, the robot will slow down and Batman and Superman will jump on.
Part 2 is the fight to destroy the main engines. First, destroy a helicopter hovering over the robot and when it crashes, its remains can be used to build a batsuit pod. The suit will be Batman's Power Suit. Use the rockets to destroy the first vents and then get Superman to destroy the undervents. Then, use the super strength on either character to pull open the vent, therefore destroying the first engine. Repeat with the second one and then the final cutscene will begin. Lex Luther gets out of his seat and when Superman goes to approach him, he will open a hatch full of Kryptonite, causing Superman to fall out of the sky. Batman then avoids a few shots from Lex, and dives off the robot. He catches Superman, and then see's the robot fall from the sky in the distance.