GAMESHARK CODEZ

I Haven't tried this out because I don't have gameshark! But you can always try it...

THE SEPHIROTH CODE........
PLAY AS SEPHIROTH 8009CBDE-FF0A 
THIS CODE CAN ONLY BE USED ON ON DISC ONE OR TWO.
START THE GAME WITH THE CODE ON,
THEN WHEN THE TITLE SCREEN APPEARS,
TURN THE GAMESHARK OFF.
LOAD A SAVED GAME ON THE FIRST OR SECOND DISC.
GO TO THE PHS AND REMOVE THE THIRD CHARACTER FROM THE PARTY SELECTION SCREEN.
TURN THE GAMESHARK BACK ON AND SEPHIROTH WILL APPEAR.
NOW TURN THE GAMESHARK OFF AND SAVE YOU'R GAME AND YOU'LL ALWAYS HAVE SEPHIROTH.
[this code always worked but he would never show up in battle and he would just die]

No idea if this works as I haven't tried it but you never know............