The Bad Unicorn Trilogy

Max Spencer is the only person in the universe who can read the Codex of Infinite Knowability—a powerful spellbook. When the Maelshadow decides he wants the book for himself, he sends Princess the Destroyer, a unicorn with attitude, to retrieve it. This sets in motion a race across the worlds—all three of them—as Max tries to master the spellbook, defeat the ultimate evil, and escape a killer unicorn.