Monstrox

Monstrox is Jestro's former sidekick and mentor of making him the "Baddest Baddie in the realm". He is also the main antagonist of the Nexo Knights.

role
In The Book Of Monsters, he debuts in the episode imprisoned in Merlock's Library, he talks to Jestro of making him a villain, but Jestro didn't want to hurt his friends, but the book says that he wouldn't have to worry about people laughing at him, so he grabs all of the other books he needed to summon monsters to attack Clay and Merlock, when Merlock tried to defeat them on his own, his library was destroyed, and Merlock was defeated easily, after that they went walking through a dark forest and summons a Book Keeper so Jestro doesn't have to keep carrying him around, and grab a few more books to make Jestro bad too.

In the first episode of season 3, he returns as a stormy evil cloud, and is renamed the Cloud of Monstrox.