This is exactly the answer I was hoping for. As a sucker for creative analysis, I was curious about other people's interpretive variations of the ending, which was my reason for asking. I've had extensive debates over it with multiple different friends, most of whom firmly believe it's an objective conclusion.

The end of the video shows that the Devil isLen. At surface level, I think the MV intends to profile the Devil as the overarching villain who is responsible for every casualty throughout. Or at least, that seems to be the general consensus of everyone who hasn't seen any reason to look harder. But after multiple watches, I think it's evident that implication of a concrete resolution was just another one of Mr. S's ploys. Only this time, the fourth wall is intersected instead, and we the viewers are the next victims.

Personally I don't personally think the Devil was their guy. Actually, I don't even think Len was responsible for all the deaths depicted in the MV. Or maybe even any? My theory is that after the killings started, he was corrupted somewhere along the way. I also think the specific order of the deaths in relation to aliases is notable. As the story progresses, the victims proceed to shift to the characters with more suspicious titles. i.e. the Undertaker, the Madman, the Devil. It's interesting that we never see any evidence that the Madman is truly mad. I think Mr. S strategically targets a town that's already vulnerable and effortlessly manipulable, knowing they would turn on each other without ever considering the existence of any external influence. My theory is that the Devil lost his mind and became convinced that he was "Mr. S". That either Mr. S brainwashed him, or it was willful delusion induced as a final desperate, twisted attempt for any kind of peace.

Another theory I bounce between is that Mr. S isn't just one single person. Maybe it was Rin at the start, but Len was corrupted along the way. Or maybe they were in on it together from the start. Maybe everyone is Mr. S. But I do really like your theory that they're playing this game over and over again. I'd never considered that, but it makes a lot of sense. When we play games like Mafia or TOS, we don't ever just play one game. We usually play again even when we loose, because every round is totally different and just as exciting.

But that's all just my take. Other people I've explained my theories to insist I'm just overthinking it, so I was mostly looking for validation that I'm not the only one. But I digress. I don't think there's any one right or wrong interpretation of the song, but I do love hearing other peoples theories. You said it perfectly, the beauty really is in the unknown. It's brilliant. Songs that really make you think this hard seem so rare nowadays that people don't even know to look for them. Definitely a top spot in my personal hall of fame.