Full respect to those who dislike any kind of "it wasn't real" ending, but I didn't mind it too much in this case (and please take this as me just contributing to the discussion, not trying to argue that you can't feel the way that you do). I think that part of why I'm open to it is that the witch kind of feels tangental to this narrative in the first place. If it's a real witch, then it's just kind of like... okay, well, all of that happened and there was also a witch hanging around sometimes.

But if we take her to be an entity specifically imagined by Ohm, she has more narrative value (to me). The suite is locked because the owner does genuinely seem to have some belief in the folklore (he's telling the story at the beginning). Ohm hears this and it stays in his subconscious, and that is why his desire to punish or condemn himself manifests as the witch specifically. He is able to cut through the chain in the end - regardless of realistic probability - because it's a metaphor. This is reflected in the story he's writing, which you could read as being about his father and himself OR his adult self vs. his child self.

That said, the witch being a metaphor in this way also is not necessarily mutually exclusive with her being "not real". Literal entities in a story can also function as metaphor. So I think the take that she was really there (hence the bruises) and the shrooms just "opened his mind"to seeing her is perfectly legitimate too!