To watch the computer fight against itself, begin a game in Versus mode. Pause the game and press A + B + X + Y. A tone will sound. Unpause the game and the computer will fight itself.
When you hear Goku talking, hold all buttons and rotate the directional pad in a full circle. Keep doing this until you hear a sound and Goku's voice again.
Secret Character(Future Trunks)
At the into screen where you see Vegeta and Son Goku's face enter Up, X, Down, B, L, Y, R, A.
If done correctly sound.
Super Saiyan Levels:
Yellow=Up, L, Down, Y
Blue=Left, L, R, Right
Super Blue=Up, L, Up, Y, Up, X, Up, R
Super Red=Left, R, Up, X, Right, Y, Down, L