Original Panzer Dragoon
Obtain the Original Panzer Dragoon in the Appendix of Pandora's  Box.  Then, at the main screen 
press the following cheat codes.

Invincibility:
L, L, R, R, Up, Down,Left, Right

Stage Select:
Up, Up, Down, Down, Left, Right, Left, Right, X, Y, White.

Wizard Mode:
L, R, L, R, Up, Down, Up, Down, Left, Right.

Unlock Stage Zero:
Up, Up, Up, Down, Down, Down, Left, Right, Left, Right, Left, Right, L, R.

Weapon Change:
Up, X, Right, Y, Down, White, Left, Y, Up, X.

Hard Mode Congratulation:
Up, Up, Down, Up, Left, Left, Right, Left, Down, Down, Up, Down, Right, Right, Left, Right.

View Hard Ending:
Up, Up, Down, Up, Right, Right, Left, Right, Down, Down, Up, Down, Left, Left, Right, Left.

Rolling Mode:
Up, Right, Down, Left,Up, Right, Down, Left, Up, Right, Down, Left, Up, Right, Down, Left.

Dragon Only Mode:
First do the weapon change cheat. Next, at the main screen press Left, Left, Right, Right, Up, 
Down, Up, Down, L, R.