A Satyr's Progeny — R. Peter Ubtrent

Aurora's son Aldor has been transported to The Land of the Five Rivers also and he's only eleven! However, Aldor is an avid roleplayer and thus knows all about Dragons and Elves and magic. What he doesn't know about is how vicious, cruel, and hostile adults can be and how much the Grand Wizard wants to capture him. With his new friends the Questor, the Tiefling, and a Unicorn named Twilight. Aldor starts his quest to find his sister Terri. Problem is, Aldor suddenly learns that he is now a Satyr and has the attendant Satyr lusts that comes with it....