Expendable

Enter the following during play: 
God Mode       Up, Down, Left, Right, L, R, Left, Right, Start
Level select   Up, Down, Up, Down, Up, Down, Left, Right, Right, Y 
Level skip     Y, Y, X, X, L, R, Down, Down Up, Up 
More lives     A, B, X, Y, L, R, Up, Down, Left, Right 
More credits   A, B, Left, A, B, Right, B, A, Down, R 
Grenades       Down, Down, Down, Down, Down, Up, Up, Up, Up, R 
Shields        Up, Down, Left, Right, X, Up, Down, Left, Right, Y
Instant win    L, R, L, R, Left, Right, Left, Right, Y, X