In the main option screen, MODE SELECT, hold down L and R, and continue holding L and R for the whole sequence. Press start on OPTION. In option, while still holding L and R, at GAME OPTION press: Left, Left, X, X, Right, Right, Down, Left, Left, Y, Y, Right, Right, Down, Left, Left, X, Y, Right, Right, Down, Left, Left, Y, X, Right, Right.
EXTRA OPTION will appear underneath the sound option.

To unlock Gill beat the game. On the character select screen, go to Sean and press up twice (up once from Gouki).

To play as Shin Gouki you must: Select arcade mode, Don't lose any rounds and get at least three perfects and no more than 3 "cheese" wins before you reach your last boss. Gouki comes out and kills your particular final boss. You fight Gouki instead and now you must defeat Gouki in the second round while he still has at least one super left. Gouki will then resurrect as Shin Gouki. Beat Shin Gouki (you can lose a round but you can't continue). To choose him go to Gouki on the select screen, hold start and press any button.

At the character selection screen, highlight Sean, press Up.