At the intro screen, immediately after you hear a voice talking, press Up, X, Down, B, L, Y, R, A.
Hold A + B + X + Y + L + R on controller two and power on the SNES system. Release the button after Goku's Kamekameha.
Before a fight, while the characters talk to each other, enter these codes to power-up your character and strengthen your attacks. If done correctly, your character should charge up.
1 Up, L, Down, Y
2 Left, R, L, Right
3 Down, X, Up, R
4 L, R, Up, Down, Y, X, Left, Right
5 Up, L, Up, R, Up, Y, Up, X
6 Left, R, Up, X, Right, Y, Down, L