Fight as Yang:
Highlight Yun at the Street Fighter 3 character selection screen and press any Kick
button.

Fight as Gouki (Akuma):
Highlight Sean at the Street Fighter 3 Second Impact character selection screen and
press Up.

Fight as Shin Gouki:
On Street Fighter 3 Second Impact, set the game to "Easy", time to "On", hit damage
to "High", one round, and play as Ryu. Then, in arcade mode, never lose a round,
defeat as many opponents with perfects and super finishes. You should find your half
way boss or AKA rival. Defeat him (Sean)and fight all the way to the end of the game
on your last man. Gouki will appear and hell death murder your last man. Defeat him
without losing the round. If you do, he will get up and turn into Shin Gouki. Defeat him
and not only will you get a different ending but you will get to play as Shin Gouki. To do
so, highlight Gouki at the character select screen and hold Start before you press a
button.

Fight as Gill:
Successfully complete Street Fighter 3 or Street Fighter 3 Second Impact under any
difficulty setting. Highlight Sean at the character selection screen and press Up(2). 

Extra options:
Unlock Gill and Shin Gouki. Enter the option screen of either game and hold L + R.
Keep those buttons held until the extra options appear at the end of the code.
Highlight the "Game Option" selection and press Left(2), X(2), Right(2). Highlight the
"Button Config" selection and press Left(2), Y(2), Right(2). Highlight the "Screen
Adjust" selection and press Left(2), X, Y, Right(2). Highlight the "Sound" selection
and press Left(2), Y, X, Right(2). If done correctly the "Extra Options" selection
should now be unlocked.

Full pause screen:
Pause game play, then press X + Y. 

Find Your Rival: 

Choose 2nd Impact when you have the choice of playing either New Generation or
2nd Impact. Goto Options and set the Difficulty to at least four stars. 
Now, choose Arcade mode and pick a fighter and Super Art. Now, within the first four
opponents, three of the four must be finished off with the Super Art. The 
fourth opponent MUST be finished with the Super Art. It doesn't matter which two of
the other three are finished off with the Super Art. After the defeat of the 
third opponent with the Super Art, a message will appear stating "Your Rival has
Found". You will then be challenged by your rival, with a short exchange of 
written dialogue on the VS screen.