Slowly enter one of the following codes before a match, while your character is speaking to the opponent.
1 - Up, L, Down, Y.
2 - Left, L, R, 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.
Fight As Adult Trunks
Press Up, X, Down, B, L, Y, R, A during the introduction when Vegeta fades into Gokuu. A sound will confirm correct code entry. Adult Trunks will be above Majiin Buu on the character selection screen.
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 is introduced. The "3" in the title will turn orange to confirm correct code entry.