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

This book contains the fifteen Prime Spells--the very foundation of all magic. Just drawing close to them is so dangerous that my lawyers require me to tell you that at any moment you may be electrified, frozen, torn asunder, flung into the air, incinerated, or cast across time and space. I recommend you close the book now and run away . . . 

MAX SPENCER

is the only person who can read the most magical book ever written: The Codex of Infinite Knowability. But the Codex isn't the easiest book to work with. First, the copyright warning reads that violators will be lashed to the Tree of Woe and licked by fire kittens. Second, it seems obsessed with the world-ending threat of squirrels. And third, it is keenly aware that a unicorn named Princess would like nothing more than to turn Max into a human shish kebab. . . . 
   Princess the Destroywe is one bad unicorn. She gets to turn her love of hunting and eating toward Max. Her mission: find the boy 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 time with a carnivorous unicorn on his trail, Max must find the courage to save himself, his friends, and the entire human race. . . .
   This is the first instalment in a hilarious new trilogy--be sure to read it before the zombie duck comes looking for you!