To active cheats, in the main menu, hold down the shift key and type: 

"MENSAAAA" 
You'll hear a guy say "thats what I need." After that during the game 

you can type the following cheats: 

LShift+LCTRL+A = skip level 
LShift+LCTRL+R = restart level 
LShift+LCTRL+C = continue if mission failed 
Press G = god mode 

Also, enter Neon's profile in the characters menu and type in the code 
"ZIOCLETO", once you reach a mission with neon, you will play the mission 
with his skeleton.