Otherworld Chronicles #3: The Dragon King by Nils Johnson-Shelton

My name is Merlin. I've helped Artie Kingfisher, or King Arthur II, reopen the gateways to the Otherworld and retrieve Excaliber, but I'm done with him now. The boy is meeting with my enemy, Morgiana, so I may even need to kill him. I don't care that he's assembled a new band of knights; they don't stand a chance against my immense magical powers. It irks me that the Lady of the Lake and others are helping Artie, but I don't think there's any way for him to enter the King's Gate and retrieve the Holy Grail. There are too many dangerous obstacles, but I'll still destroy him if he manages to succeed. Anyhow, he has no idea that I'm kidnapping kids using the Otherworld video game, and he has no idea about my secret plans. This boy king is merely an annoying pest.

You need to read the first books in the series. I enjoy Artie's character and how he's grown as a ruler. It's funny how his sister gets upset when he's giving orders, so he must watch how he asks her to help. The plot in this book is a complete twist from the first one. Merlin mentored and trained Artie in the first book, but now he's the main villain. I don't recall reading a series where an important protagonist became the most important antagonist in a plot. I'm not sure why, but I grew tired of the plot near the end. It still had adventure and mystery, but it just seemed like Artie was getting into one tough situation after another. Same ideas, just different obstacles. I don't know if most readers will feel the same way, and you may love it. I was probably in the wrong mood for some reason. It's a solid book.