Nightmare of the Iguana (Dragonbreath Series #8)

Danny Dragonbreath has seen a lot of weird things, but nothing quite like the inside of his best friend Wendell's brain. Wendell has been having terrible nightmares, and Danny and Wendell's totally-not-girlfriend Suki agree to venture into the iguana's mind to get rid of the thing causing the dreams--before Wendell goes permanently insane. There's more scary stuff in Wendell's strange and nerdy subconscious than Danny bargained for, and getting out of there is no easy feat, even for a ninja...