Play "The Lantern Menace" level in Free Play mode. Go to the first part, and progress from the start until you reach the point where you are facing a large Brainiac skull in a symmetrical room. On the right side is an electric field, and on the left an electric port. Switch to any character that has an electricity suit (put on infinite electricity, if desired), and fill the port on the left. This will get rid of the Brainiac tentacles on the top of the stairs, and fire should replace them. Switch to Superman, and walk in the middle of the fires. Initiate his freeze-breath to extinguish the fire and get studs for it, but the fire will immediately return. Keep extinguishing the fire with Superman to get as many studs as desired. Use any stud multiplier to make this even more effective.