The Battle to Determine King of the Mamodo World (魔界の王を決める戦い, Makai no Ō o Kimeru Tatakai), or simply Mamodo Battle ("Demon Battle"), is a battle of all the Mamodo to decide the future Mamodo King. This tournament takes place every thousand years. During the fight, Mamodo fight with humans who use their spell books to fight with spells they remember from the Mamodo World. They send 100 Mamodo children to fight. Two known winners are King Bell and his son Zatch Bell. The Headmaster, who is one million years old, decides who competes in the competition. When a child's book is burned, they return to the mamodo world with just their soul without their body until a winner is chosen. The winner gets to manipulate the whole Mamodo World (such as changing laws or wiping out all or certain Mamodo). The children are sent all over the world to find their partners and fight.
Previous Battle to Determine King
This Battle to Determine King of Demon World took place during the Middles Ages (Year 100X A.D., where X could be any number). 57 known contestants during this battle were turned into stone tablets by Goren's Dioga Gorugojio spell and were not send back to the Mamodo World (they stayed in the human world) until the middle of the next Mamodo Battle. However, they were still considered to be "eliminated" during this millennium's Mamodo Battle even though they weren't send back to the Mamodo World.
- King Bell (winner)
Current Battle to Determine King
See also: Mamodo Battle Ranking
This Battle to Determine King of Demon World took place during the contemporary history of the Modern Ages (Year 200X A.D., where X could be any number). While a majority of battles were shown in Japan, many battles took place all over the world. Many of the previous contestants from the previous Mamodo Battle who were turned to stone by Goren of the Stone were cured during this battle a thousand years later by Zofis and Koko and they were given new partners, which may be their old partners' descendants.
- Arth (10th place-Book Burned by Goomu and Mir) (manga only)
- Ashuron (9th place-Book Burned by Clear Note and Vino)
- Brago (2nd place-Book Burned by Zatch Bell and Kiyo Takamine)
- Clear Note (3rd place-Book Burned by Zatch Bell and Kiyo Takamine)
- Goomu (6th place-Book Burned by Zatch Bell and Kiyo Takamine at Mir's request)
- Kanchomé (7th place-Book Burned by Clear Note and Vino)
- Ponygon (4th place-Book Burned by Megumi Ooumi at Sunbeam’s request)
- Purio (8th place-Book Burned by Clear Note and Vino)
- Tia (5th place-Book Burned by Clear Note and Vino)
- Zatch Bell (winner)