So, there is Jacob and the MiB/Smokey, but who was in the cabin? It was surrounded by ashes, so Jacob or someone is trapping somebody in there.
It can't be the MiB/Smokey because he appeared to people as ghost or as Smokey since season 1.
And whatever is in the cabin is set free because there is an open area in the ashes.
What do you think it is?