Defeat the Fire Robots on Killer Expo
To defeat the fire breathing robots that are blocking the secret lab at the end, all you do is hit the robot at the beginning of the battlefield. There's only one of them so it shouldn't be to had to find. If you hit it with a star it will shoot its hands at you. Shoot it a couple of times and it will start to chase you. Lead it to one of the robots and it will destroy them, giving you access to the lab where the machine that you are looking for is.