Bad Unicorn - Platte F. Clark (Bad Unicorn #1)

Goodreads 3.71

In this start to a hilarious middle-grade fantasy trilogy, Max Spencer discovers that a killer unicorn is hunting him.

It wasn't Max Spencer's idea to fight robots, lead an army, or save the world—it just so happens that he's the only living person who can read the most fantastical book ever written: The Codex of Infinite Knowability. The Codex is no ordinary book, and among other things, it describes a unicorn named Princess the Destroyer. 

Princess the Destroyer is no ordinary unicorn. She loves nothing more than hunting down, killing, and eating other creatures. After all, what's the point of having a sharp horn on your forehead if you don't use it for destructive purposes? And right now Princess has a very definite purpose: Find Max and retrieve the lost Codex for an evil sorcerer and his mysterious master. If she can do that, she's been promised an all-the-humans-you-can-eat buffet in Texas.

Stuck in another world and with a carnivorous unicorn on his trail, Max must find the courage to save himself, his friends, and, oh yeah...the entire human race.