A horror movie with deeper themes than the standard possession story, "The Wailing" isn't the kind of film that ties up every loose end with a nice, neat, little bow. On the contrary, the ending of the film is confusing, with plenty of unanswered questions that leave it up to the viewer to decide what it means. However, there are a few answers given in the film's final moments, not the least of which is the true identity of the demon.
The shocking twist delivered by Il-gwang — that the demon was in fact the woman in white, Moo-myeong — wasn't the truth. When Yang Yi-sam confronts the Japanese man, it is revealed in no uncertain terms that he is truly a ghost — a demon in the guise of a man. As the deacon stands stupefied before him, we witness the Japanese man transform into something resembling his true form: A charred, deformed being with long nails, sharpened teeth, and blood-red eyes.
As for Moo-myeong, it's not revealed who or what she really is, though Il-gwang's false revelation suggests she was, in fact, the true shaman out to banish the demon forever. As for Il-gwang, it seems that he had been corrupted by the demon, and was helping it kill the people of Gokseong. He is seen at the end taking photographs of Jong-goo and his possessed daughter, presumably to add to the demon's collection.
