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.
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":
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:
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