
Also, what do you think about the fact that Yeonwoo hide his face? Could there be a reason why he insisted on being anonymous? One time when Taejun's friend took his phone without consent, he got really angry and destroyed the phone until there is no evidence of his face. He have no problems if people see his face, but not when it's in a picture.

i think with the phone thing it might create another "version" of him because there is already another version of him that he was talking to in the mirror or maybe taking pictures of him would anger his reflection or something like that because a picture is pretty much your reflection frozen forever. ╮( ̄▽ ̄)╭ but i don't rlly know
I think, Yeonwoo could be part of a cult that involves mirror worshipping. Those who died, their bodies become foods, as an offering for the worshipped (I presume, the devils). But the bodies do not necessarily disappear, as it became part of the devil's, and it's also something Yeonwoo could control. Because, we see sometimes there are hands crawling around. The body parts are there. The reason why I think Yeonwoo could control it is also due to the cinema incident. To summarize, he can commit murder then feed it to the devil.So it's like a symbiotic relationship.
My question is though, when did this start? Probably, when he was a child since we know his parents died in that room with the same kind of murder method (evaporated). But how? With the help of whom? Did the devil showed up at the moment? What could Taejun contribute at that moment? Until the black room is exposed, I can only give speculations. Please share your guess!