Type during the game

 GONZOANDJON

 and now you have the following keys (Alternatively use GONZOANDJON as
 your players' name):

 [Shift][X]       - Teleport
 [Crtl][V]        - Invisibility
 [Crtl][-]        - Frame rate
 [Crtl][Shift][N] - End mission
 [Crtl][Shift][X] - Kill all enemies
 [Ctrl][I]        - Invulnerability

 ---

 Levelcodes:


        Normal  Hard     Hardest

   01:   XHGDR  PLKUM    PVTSL
   02:   WKUC4  JE5SH    SKDJF
   03:   YSM51  DFY3B    3DYNG
   04:   B7D8F  K9D3H    9BG3S
   05:   3GHSL  NMWQ9    KJWJK
   06:   AZLM1  16G3L    E2J7H
   07:   JAHSG  WL3CZ    ZX78Y
   08:   UN63A  LPQ6T    TRIB4
   09:   VAZ2P  SRCM8    TRD78
   10:   9TT5W  PAEN8    1LPQD