
It reminds me about ”And Then There Were None” by Agatha Christie which has inspired several movie adaptations. https://en.m.wikipedia.org/wiki/And_Then_There_Were_None

Guys, I wrote this when I was only at the chapter 20 when Bada was still the main player so I thought he could be the killer himself without him knowing, I thought of this based on a movie called '' Triangle '' where the main character was stuck in loop of repeated deaths, her name was Jess, she dies the first time then she wakes up in a yacht with her friends at the departing point just like Bada wakes up in the car, then they have a yachting accident after that they find an abandoned cruise liner that they take refuge in and the killing starts (before they get on the cruse Jess sees someone on it looking at them and then disappears) , the killer was wearing a bag as a mask on his head just like the manhwa killer, he was stalking Jess specifically and in the process of trying to kill her her friends dies one after the other until the killer finally kills her and she wakes up again at the departing point in the same yacht with the same people, same dialogs and the same scenes but she keeps her memories from her first death then the same scenario of deaths repeats and now she is trying to survive but she dies and wakes up agains multiple times the only thing different from the manhwa is that when the get on the cruse their dead bodies are still there and Jess is the only one that discovers them because she knows the spot where everyone of them die and how they die, she figured then that she could be the cause of this loop so she kills all her friends including herself then goes to the deck waiting for the next loop to start bringing the new yacht with new her and starts trying to kill her new self, this when she realizes that she is the killer and that she is the person she sees every time they approach the cruise line.
But, after reading further chapters in the manhwa it is revealed that all the characters in the game are players not just NCPs which means the idea of Bada being the killer is no longer valid cause anyone of them could be the killer and they could all be killers, each one of them is playing the game in his own way and trying to get as much endings as they could.
I think I figured out who is the killer, if I'm not wrong this story is similar and maybe inspired by a movie that has the same context. I won't say who I think the killer is cause it could be a spoiler but if any one is interested or curious to know what I'm talking about tell me in a comment below.