Turns Out I'm An Alien - Lou Treleaven - Bog

Jasper thinks his life is as normal as can be (green hair aside) until he discovers his foster parents have been witholding a pretty huge secret from him. His green hair isn't just a perculiarity but a trait of a Prince of Glooop, a slime-covered planet in the Triangulum Galaxy. When Earth is under threat from the Emperor Iko Iko Iko, Jasper and his foster sister, Holly, get pulled into a rather crazy adventure in space. Things get even crazier when he discovers he has a superpower... but not super strength or super speed ... nope, he can turn into a slug. He just wants to liberate his home planet, foster galaxy and save his parents.