Zatch Bell! Mamodo Battles

Password mode:
Defeat the first ten opponents in Zatch Bell's story line to unlock the password option in the Bonus section.
Zeldarulah.

Play as Laila and Albert:
Enter UCKAHEIT as a password.
Zeldarulah.

Alternately, buy all Event cards in bonus mode. To unlock Leila and Albert (waking), buy all Partner cards in bonus mode.
bsoi ebpoi tpiy.

Play as Victoream and Mohawk Ace:
Enter THECZBALL as a password.

Alternately, buy all Mamodo cards in bonus mode.

Play as Zeno and Dufort:
Press Up(2), Down(2), Left, Right, Left, Right, B, A at the title screen.
Zeldarulah.

Play as Zeno and Dufort in story mode:
Press Up(2), Down(2), Right, Left, Right, A, B at the title screen.
Zeldarulah.

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.
Zeldarulah.

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.
justinz.

Alternately, complete Time Attack mode with any character. Getting the powered-up version of a character helps.
Zeldarulah and Jake.

To play as Ponygon, reach him in Time Attack mode in under eight minutes and defeat him.
camroots.

Play as Wonrei and Li-En:
Defeat Wonrei and Li-En in story mode.
Zeldarulah.

Play as Zeon and Deufo:
Complete Zatch story mode to unlock Zeon and Deufo as selectable characters.

Hint: Powered up forms:
To get in a powered up form you must win the first two rounds.
Oscar Trusty III.

Hint: Powered up Bari:
Complete Power-Up Time Attack mode as a powered-up character with a time less than 8:00.

Hint: Powered up Brago:
Complete level 52 (Don't Disappoint Me) in Zeno's story line, then go to Mochinoki Park.

Hint: Powered up Kanchome:
Defeat Kanchome two times, Brago once, and Bari once in Tia's story line, then go to the Circus Tent.

Hint: Powered up Kido:
Complete Zatch's story mode. Then, go back into his story and go to Mochinoki Park. He is not very difficult, but he counters frequently.
zaker_zaker.

Hint: Powered up Laila:
Successfully complete Power-Up Time Attack mode as normal Laila.

Hint: Powered up Waking Laila:
Successfully complete Power-Up Time Attack mode as normal Waking Laila.

Hint: Powered up Milordo-Z:
Successfully complete Power-Up Time Attack mode as normal Milordo-Z.

Hint: Powered up Ponygon:
Defeat Ponygon at Mochinoki Park and Kanchome at the Department Store. Then, go to Mochinoki Middle School.

Hint: Powered up Tia:
In Kanchome's story mode, defeat Ponygon at the Park. Then go to the Quarry. Folgore should say "Look, a Mamodo!". Tia is the easiest powered up character to get.
zaker_zaker.

Hint: Powered up Victoream:
Successfully complete Power-Up Time Attack mode as normal Victoream.

Hint: Powered up Wonrei:
Play as Wonrei in story mode. After defeating Zatch at London Suburbs, go to Fairy Woods. Powered up Wonrei is fast, but besides that is easy to defeat.
zaker_zaker.

Hint: Powered up Zatch:
To find powered up Zatch, as Kanchome defeat Ponygon at the Park. Then immediately go to the river bed. He is semi-difficult.
zaker_zaker.

Hint: Powered-up Zeno and Dufort:
When playing Zatch's story mode, after you defeat Ponygon at Fairywoods, go back. Zatch should say, "Hey, who are you?". You will then fight a powered-up Zeno. If you lose, you can go back. This battle is very difficult.
zaker_zaker.

Hint: Powered up Zofis and Bari:
Complete Powered Up mode in Time Attack for the first time. To get Powered Up mode, defeat powered up Zatch.
zaker_zaker.

Hint: Other characters:
Defeat the following characters in Story mode to unlock them as playable.

Belgim E.O.
Demolt
Laila
Pamoon
Penny
Tsao-Lon.

Hint: Partners in Model Gallery:
Successfully complete Arcade mode with the following characters to unlock them in the Model Gallery.

Zatch
Reycom
Sugino
Kolulu
Fein
Eshros
Robnos
Maruss
Brago
Rops Baransha
Bari
Kido
Tia
Kanchome
Hyde
Wonrei
Victoream
Ponygon
Zeno

Hint: Mamodos in the Model Gallery:
Defeat the following Mamodos with an "A" rank in Story mode to unlock them and their partners in the Model Gallery.

Baltro
Penny
Byonko
Laila
Tsao-lon
Belgim E.O.
Pamoon
Demolt
Zophis

Glitch: Li-en's dress:
When fighting powered up Wonrei, the opponent Li-en's dress is red. It is supposed to be blue because you are fighting the same Mamodo as you. This applies even if you are powered up.
zaker_zaker.