Start game as usual, during gameplay go to the Secret codes menu and
use the following codes:

Unlock - Unlock All Missions (MasterCheat)
GazerBeam- Shoot Beams For A While
SmartBomb- Kill Enemies And Every Item Near You 
SassMode - Game Becomes Faster
UUDDLRLRBAS- Refill 25% Health
Showtime - Get Incredipower For A while 
DanielTheFlash - Get Incredipower For Superspeed - Press
 Right Mousebutton While Running
McTravis - Get Incredipower - Press Right Mousebutton 
 For Fast Running And Ramming Everything
Kronos - Get Windtrails And Superpunch
AthletesFoot - Enable Fire Trail
BWTheMovie - Toggle Player Slowmotion 
InvertCameraX- X Cam Controls Change (Mouse)
InvertCameraY- Y Cam Controls Change (Mouse)
Einsteinium- Large Head 
DeEvolve - Small Head 
bHUD - Toggle Hud 
BoaPlace - Nothing
RotAIDalg- Nothing
Hi - Show Intro 
YourNameInLights - Show Credits 
TheDudeAbides- ?
SpringBreak- ?
PinkSlip - ?
Labombe- ?
InvertTurret - ?
EMode- ?
DiscoRules - ?
Dandruff - ?
TonyLoaf - ?
Flexible - ?
DashLikes- ?

Notice that some codes only work on certain levels/missions.

To enable MasterCheats you must first add "AllowMasterCheats = 1" 
(without the quotes) on a separate line to your .\Game\in.ini file
then restart game. The way to know that AllowMasterCheats has been
correctly activated is by looking for debug info during gameplay, 
namely game build version aswell as a FPS counter will show on screen