Press Down(10) before the match as the characters are speaking to one another.
Decipher the code for the secret characters
During story-mode choose any of the four characters and set the difficulty to level 3 or higher. Now, go through the story without losing and you'll be challenged by Broly after beating Bojack. Once you win, you'll then get a secret ending screen with a number followed by two letters. Each of the four playable characters get their own unique combination. The number points to where the two letters that follows it fit into the full secret password. Once you've aquired all of the ending passwords and combined them, input the completed sequence while Gohan is flying to the lookout to unlock the two secret fighters.
Unlockable
How to Unlock
The first sequence
Beat Broly as Gohan
The second sequence
Beat Broly as Vegeta.
The third sequence
Beat Broly as Trunks.
The fourth sequence
Beat Broly as Piccolo.
Fight As Brawly Against Goku
Wait until Son Goku's hand flies toward the tower in the sky during the introduction sequence. Then, press Up, X, Down, B, L, Y, R, A. A sound will confirm correct code entry.
Forfeit Match
Hold Y + X + B + A and press Select during game play.
Turbo Mode
Hold L + R when the hands appear during the introduction sequence.
View Moves
Press Start to pause game play, then press Select. Press Down(2), then press A to display a move list for the current fighter. Highlight a move and press A to practice.