To unlock the extras go to options and select extras and enter codes:
Unlock Lancers Cyclone (Multiplayer): YLLWFLLW
Unlock Rands Cyclone (Multiplayer): KIDGLOVES
Invincibility (Single Player Only): SUPERCYC
Unlimmited Ammo (Single Player Only): TRGRHPY
Unlock All Levels (Single Player Only): RECLAMATION
Unlock Scott Bernards Cyclone (Multiplayer): LTNTCMDR
Unlock Rook Bartleys Cyclone (Multiplayer): BLUEANGLS
One Hit Kills (Single Player Only): DUSTYAYRES
Note All Passwords Are Case Sensitive.
Defeating Larger Enemies
When fighting the bigger enemies, aim for the eyes.
Falling protoculture
Once you got all the maps go to level tasha hive 1 or 2. Then get to the part where you fight the boss shoot the core the big thing. Right above you and protoculture will fall. you can shoot with any weapon.
Jack Archer Lives
After you beat the game, use the unlock all levels code and start a new game and select the Bygone Marshes (or just start a new game without the code and get to that level).
Turn around at the very start and there is a long area that you can drive through. So, drive through the pillars until you get to the last two sets of pillars. On one of them (facing north-east [use your compass]) there is vandalism that says, "Jack Archer Lives!!"
If you shoot that particular sign, a health pack will drop, followed by protoculture, then a Holden Mark-2 Shotgun. There's one more item that comes out, but you have to keep shooting the sign until it does. If you do, you'll get a soccer ball. You can shoot it with the shotgun to make it bounce all over and test out the Havok physics engine.
Unlock Third Ending
During the fight with the Invid princess (Reflex Point), turn on the THERMO scanner. There is bright yellow spot on her right shoulder (everywhere else is blue). It's hard to hit, but it's the only spot that's not covered by her freakin' overshield. By killing the boss through this way, you unlock the third ending.