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 Uri that 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.
Alvin was a grumpy, old man from Madagascar who was trying to live out the rest of his life in peace by himself at his cottage located somewhere in a valley. One day he discovers Byonko who asks him to join him in his fight fo king, however he declines which makes Byonko very upset. He is intrigued by the four leaf clover on Byonko's head calling it a "salad," and picks one of the leaves turning it permanently into a three leaf clover as a result Byonko gets more upset and cries even more. Alvin decides to team up with Byonko to make him "cool".
However, he does realize the intentions of Zofis and hence removes his false teeth, rendering him unable to use his spells properly and hindering himself and Byonko. However, once Byonko realizes the true nature of Zofis and switches over with Penny to Zatch's side, he puts on the false teeth once more, allowing Byonko to fight. He shed tears during his and Byonko's parting; when Byonko asks Alvin if he was "cool," Alvin responds that Byonko is "super cool."