Play as Zeno and Dufort:
At the title screen, press Up(2), Down(2), Left, Right, Left, Right, Circle, X to unlock Zeno and Dufort.

Play as Zeno and Dufort in Story mode:
At the title screen, press Up(2), Down(2), Right, Left, Right, X, Circle to unlock Zeno and Dufort in Story mode.

Password option:
Defeat the first ten opponents in Zatch Bell's story line to unlock the "Password" option under the Bonus section. Enter one of the following passwords to active the corresponding cheat function:

Play as Laila and Albert:
Enter "UCKAHEIT" as a password to unlock Laila and Albert. Alternately, buy all Event cards in Bonus mode.