I remember quite a while back I watched a Goosebumps episode where some kids found a mirror that would bring their evil clone out in the attic or something like that, but I don’t know the name.
The episode is "Let's Get Invisible!" (1996), based on the book.
Max, his brother and his friend, Erin, discover a mirror which has the ability to turn them invisible. They have fun playing around with it at first, until the mirror starts to show a malevolent side.
That night when everybody was supposed to eat dinner, Noah became invisible. He ate and drank his dinner while he was invisible. His parents were looking everywhere for him. Max took him upstairs back to the attic and made him visible again. When he came back, Noah was strange. He talked different and he acted different.
Later, Max came back from Baseball practice. But when he came home, Zack and Erin were upstairs in the attic playing with the mirror and becoming invisible. Zack was invisible and then he starts to feel dizzy and cold, and his voice was weird. When he was visible, he started acting strange like Noah. He made Max invisible. Then somehow, Max was pulled into the mirror in a weird dimension. He saw his reflection there talking to the Real Max. Erin saw that Zacks earring was on the wrong ear. Max's reflection kept talking about him taking Max's place and making the Real Max trapped in the mirror, but Max didnt want to. Erin pulls the cord and after a long period of time, Max came back...halfway frozen. He told Erin to break the mirror. When she did, everything went back to normal. But after the group left the room...the mirror fixed itself.
When the Dad asked Noah to throw him something, Noah threw it with his right-hand. Did he and his reflection switch???