Go to the main menu, hold L and and press Right, Right, Left, Left, Down, Up, B to unlock everything.
Enter the codes below at the main menu to unlock the effect needed:
Slow Deaths: Up, Up, Down, Down, X, Y, Y, X, Up, Up, Down, Down, X, Y, Y, X
Toggle Infinite Supers: Up, Up, Down, Down, A, X, A, X
Toggle AI: Up, Up, Down, Down, A, A, B, B, X, X, Y, Y
Toggle One Hit Deaths: Up, Up, Down, Down, X, Y, Y, X