enter these cheats in the cheat menu and a messege will appear to confirm correct entry.

infinite superpower:
JOR EL

infinite health:
SMALLVILLE

unlock everything:
MXYZPTLK

unlock movies
LANA LANG

unlock biographies:
LARA

unlock hard mode:
BIZARRO

when you have worn mettallo down enough so that he gets stuck on the magnetic floor, quickly fly up and use your heat beam on the switch to your right. This will end the game and take you to the ending FMV sequence. You may need to try this a couple of times as you may find it difficult to get there and activate the switch.

Select Cheat Codes from the Options menu and enter the following

Master Code - MXYZPTLK