Start a game and pause it. While the game is paused, press Top C, Bottom C, Left C, and Right C. A new option, Cheat, should appear. Move the arrow next to Cheat, and press A. To access the cheats, press the following buttons:
Clipping: Press Top C 20 times, Bottom C.
Butcher: Press Bottom C, Top C, Left C, Left C.
God Mode: Press Left C, Right C, Bottom C.
Health: Press Left C, Top C, Bottom C, Bottom C.
Visit: Press Left C, Left C, Right C, Right C, Bottom C, Top C.
Enter the sub-menu, Collect, and press the following buttons to do these cheats:
All Artifacts: Press Top C, Right C, Bottom C, Bottom C.
All Keys: Press Bottom C, Bottom C, Top C, Left C, Right C.
All Puzzle Items: Press Top C, Left C, Left C, Left C, Right C, Bottom C, Bottom C.
All Weapons: Press Right C, Top C, Bottom C, Bottom C.