Pause the game, then press C-up, C-down,C-left, C-right Press C-up 20 times, and then C-down once - Clipping mode.
Press C-left, C-right, C-down - God mode.
Press C-left C-up C-down twice - 100% Health.
These codes can be entered anytime:
Press C up C left 3 time's C right C down twice -All puzzles.
Press C-right C-up C-down twice - Full weapons.
Press C-down C-up C-left C-right - All the keys.
Press C-up C-right C-down C-up - Full Artifacts.
Press C-left, C-left, C-right, C-right, C-down, C-up - Level Warp.
Press C-down,C-up,C-left,C-left - Kills everything on the level.