The Window : Billdip

There was something not quite right about the window in their room.

After defeating Bill, Mabel and Dipper had returned home and continued life as normally as they could. The only differences being that Mabel now thought through plans more thoroughly and Dipper had become more adventurous and confident. They had both been through horrible things in Gravity Falls, but that didn't stop them from going back every summer.
And every summer, the feeling that something was off increased. Dipper was the first to notice it on their fourth summer back.