I don't think the room leader is big mouse. Why? Because episode 11 ending made us think that he is Big Mouse.…
I think it should mainly make sense, when the whole story is revealed. Like people saying it's Min Ho... That would make zero sense, it would just be shocking. So I don't really get who should it be, to be both shocking but also it would make sense.
I hope that BM is really the room leader, it would make the most sense to me (he worked along Chang Ho, the possible motive of revenge for someone close would add up for his missing/dead daughter) But maybe it is process of elimination and at the beginning of tomorrow's ep, we will be mislead again.
I really hope it will begin to air this year. The shooting is taking so long, but at the same, there will probably be a lot of special effects and so. Still, hoping for 2022 release 🤞