"Zero to Hero (Ghost Buddy Series #1)," by Henry Winkler and Lin Oliver
Synopsis: Billy Broccoli is new to the neighborhood, and wants cool friends and a spot on the baseball team more than anything. But the one thing he never wanted is his own personal ghost. So imagine his surprise when he ends up sharing a room with Hoover Porterhouse, a funny ghost with a whole lot of attitude. When an obnoxious school bully sets out to demolish Billy, the Hoove comes up with a plan for revenge. It’s all in the Hoove’s Rule Number Forty-Two: Stay cool. And like it or not, Billy and the Hoove have to stick together if Billy ever wants to get in style, get even, and conquer the school. - Scholastic Inc.