Defeat the first ten opponents in Zatch Bell's story line to unlock the password option in the Bonus section.
Play as Laila and Albert:
Enter UCKAHEIT as a password.
Alternately, buy all Event cards in bonus mode. To unlock Leila and Albert (waking), buy all Partner cards in bonus mode.
Play as Zeno and Dufort:
Press Up, Up, Down, Down, Left, Right, Left, Right, B, A at the title screen.
Play as Zeno and Dufort in story mode:
Press Up, Up, Down, Down, Right, Left, Right, A, B at the title screen.
Play as Maestro:
In the Japanese version, win Time Attack mode 300 times to face Maestro. Defeat him to unlock him as a selectable character.
Play as Milordo-Z and Koko:
Buy all Spell cards in bonus mode.
Play as Dr. Riddles and Kido:
Defeat Mr. Riddles and Kido in any story mode.
Play as Ponygon:
To unlock Ponygon, you must first get the powered-up version of Brago and Sherry in Zeno's story. To do this, after defeating Brago and Sherry in Zeno's story, go to the park. Defeat powered up Brago/Sherry, who are encountered randomly. Then, complete Zenos story, which will unlock powered up Brago/Sherry. Afterwards, use powered up Brago in time attack mode on normal opponents, and not the powered up version if you have it. The last level you do should be Ponygon. Defeat him, and at the end of time attack mode, you should unlock him. Ponygon has no spells. If you try to use one, a "?" will appear on his head.
Alternately, complete Time Attack mode with normal Brago and Sherry.
Play as Victoream and Mohawk Ace:
Buy all Mamodo cards in bonus mode.
Play as Wonrei and Li-En:
Defeat Wonrei and Li-En in story mode.
Play as Zeon and Deufo:
Complete Zatch story mode to unlock Zeon and Deufo as selectable characters.