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).