We all know Season 5 is gonna be about Will and his journey, with flashbacks about his time in the upside down. We know this from the BTS photos. I have a theory regarding unreleased footage dating all the way back to S1 E1. If you go back and look at the still images that go with the episodes on Netflix (Tv not smart phone) they all include actual shots that are included in that episode, every one EXCEPT S1E1. When will is running away from the Demogorgon he just runs straight to the shed and slams the door behind him, he then waits for it to arrive with a shotgun. In the still image, he is standing outside it observing the glowing light from the shed in what seems like a calm manner. I believe this may be after he vanished along with the Demogorgon, and I think Vecna is subjecting him to a vision.