Press the '~' (tilde) key during gameplay to bring down the console to be enter the following codes. Press 'Enter' after the code has been entered to activate it.

Unlock the Cheats Manager so different cheats are available through the 'Pause' menu:
Enablecheats

Invincibilty and pressing the number keys will spawn Weapons and Upgrades:
Cheatdeath

Change Gravity - Default is -1400:
Setgravity (number)

Make the NOED open it's Mouth:
Hurtnoed

Give Blitz Full Health:
Givehealth

Make Blitz Dance:
Dance

Blow Yourself Up:
Selfdestruct