Let's Get Invisible! by R.L. Stine
They're baa-ack! Make way for the bestselling children's series of all time! With a fresh new look, GOOSEBUMPS is set to scare a whole new generation of kids. So reader beware--you're in for a scare! On Max's birthday, he finds a kind of magic mirror in the attic. It can make make him invisible. So Max and his friends start playing now you see me, now you don't. Until Max realizes that he's losing control. Staying invisible a little too long. Having a harder and harder time coming back. Being invisible is turning into a very dangerous game. The next time Max gets invisible, will it be... forever?