Cheats:

 Press together

 [Z][E][U][S] - God mode
 [N][E][X][T] - Warp mode
 [X][T][R][A] - Increases ammo

 Attention, there is another trick. To activate the warp and ammo mode
 first release the third key after this all the others.
 When you are in god mode you can press [G] to deactivate the gravity.