Original Concept FMV sequence:
Successfully complete the game in campaign mode. 

Multi-player General Corrosive:
Successfully complete the game with all secret and speed chips to unlock General 
Corrosive as a playable character in multi-player mode. 

Cleaner in level 15 Minutes:
 
In the level 15 minutes, the old droid in the jail cell will talk to you, when the mils 
come to get you, hit them with you're arm until they start shooting at you, when 
they do this hide behind the old droid and the mils will destroy him instead of you 
and a cleaner should appear! Now use it against those Titans! 

Fighting the Zombiebot King:
In order to beat the Zombiebot King just wear him down using rockets until he 
pauses (doesn't move). Toss a grenade (coring charge) into its mouth. On Normal, 
it takes five grenades to kill him and after the 3rd and 4th grenades there are 
regular zombiebots that swarm the arena.