Fall through floor
Play the rooftop level just before the intermission of Max blowing up the satellite tower under the normal difficulty setting. At the start of the level, run and collect the items in the wall. Do not sneak up on the first man; he must turn and see you. Walk behind him when he stops. Wait until he turns around, then press [Y] to flip him. This will cause you to fall underneath the floor and bypass all the guards. Run to the end of the level where the final locked gate is located. Run into it to complete the level without running out of time or being seen by the guards.
Submitted by: Gaius
Extended ending:
Successfully complete the game and wait for the credits to end. An extended sequence featuring the game's true ending will begin.
Submitted by: Gaius
