Need help finding name of a sci-fi book I read in elementary: Only remember Aliens

[elusiveminds]

and yellow dog? Ok so this is a long shot. Basically back in elementary I read a book that was on a shelf for SSR. I dont remember much or the details but I know its about a kid who meets an alien. The alien tells him to help him fight off this other alien who comes around, telling the boy he is the "bad alien" The boy helps him, I remember breaking into houses with credit cards and maybe a yellow dog, perhaps a golden retriever, i dont remember if the dog was alien or not. The twist at the end is that the alien the boy is helping is in fact the "bad alien"! Thats all I remember hope someone can help me.