Byonko (ビョンコ, Byonko) and Alvin (アルヴィン, Aruvin) are two fictional characters in the manga and anime series Zatch Bell!, and two of the major antagonists in the series along with Penny and Urithat join Zofis but later turn good towards the end of the second season.
Byonko is a talking frog mamodo from the Mamodo world. Byonko himself gets upset very easily and is always worried especially about making friends. During battle he is shown to be complimenting himself on how good his skills are instead of worring about the enemy. At some point he befriends Zofis and assists him in collecting the Ancient Mamodo that were locked away in stone tablet but Zofis could revive them as his servants. Thinking that he and Zofis were friends, he along with Penny joined Zofis and became his first two assisstant duos for the Ancient Mamodo. They held power over the ancient Mamodo and would give orders to them to attack and destroy Zatch and Kiyo along with their other friends.
Byonko's abilities are mainly slime based which matches up with his frog personality perfectly. It mostly has to do with stretching his limbs or shooting out bubbles made out of slime. He is also shown to be extremely strong being able to knock down Demolt.
- Although Alvin's true age is never revealed, it can be assumed that he is the oldest Book Owner to appear in the fight.