Clip Off/On
     Press C-Up 20 times, C-Down.

All Puzzle Items
     Press C-Up, C-Left, C-Left, C-Left, C-Right, C-Down, C-Down.

Various Cheats
     First,  enter  C-Up,  C-Down,  C-Left, C-Right, a cheat menu will
appear and go into it to enter any of the following "Codes":

Effect                  Code
God Mode                C-Left, C-Right, C-Down
Level Select            C-Left, C-Left, C-Right, C-Right, C-Down, C-Up
Butcher                 C-Down, C-Up, C-Left, C-Left
Health                  C-Left, C-Up, C-Down, C-Down
No Clipping             C-Up(20x), C-Down

More Various Cheats
     Enter these at the Collect Sub-Menu:

Effect                  Code
All Keys                C-Down, C-Up, C-Left, C-Right
All Artifacts           C-Up, C-Right, C-Down, C-Up
All Weapons             C-Right, C-Up, C-Down, C-Down