Fighting Carpenter
When you are trying to beat carpenter, use martyr and make sure you have a flame thrower and rocket launcher. As soon as you get to him, use the rocket launcher to blow up the electric chair (about 6-7 direct hits) then switch to the flame thrower. Run like heck and spray him with the flame thrower when he stops to try and cut you. Takes a little while but i found this technique to be the most effective.

All weapons
Press B, Up, Left, Down, Right, B(2) during game play to get the best version of each weapon. Note: The directions are done on the D-pad. This code can only be enabled one time.

Sound test
Press Left(2), B or Right(2), B during game play.

Nightmare mode
Successfully complete the game to unlock the "Nightmare Mode" option at the Special Features screen.

Alternate Hunter mode
Successfully complete the game to unlock the "Alternate Hunter Mode" option at the Special Features screen.

Alternate ending sequence
Save at over 50 Innocents before returning to the train to unlock the good ending.