To have the characters play in Full-Turbo Mode, hold A+B+X+Y+L+R on controller two and power on the SNES system. Release the button after Goku's Kamekameha.
To get extra characters, go to the the intro screen, immediately after you hear a voice talking, press Up, X, Down, B, L, Y, R, A.
To have the characters play in Half-Turbo Mode, hold L+X or R+X button before turn ON / reset console until Title screen. If correct, the ball color behind number "3" will become Blue.