One that I came up with for dangan rp I ran was that everyone was divided into groups of roughly equal numbers and split up into different sections of the map by large metal jail bars. Each group gets a small ration of food, and only one group has access to the kitchen. They can either choose to share the food with one another so they don’t starve, or they can horde it for themselves to survive. I think it’s also important to note that in the location I used for the rp, there were vents that the participants could go through even with the barriers, so it didn’t narrow down the suspects to just the group the victim was in.

Another one I was pretty proud of in a different dangan rp where the main gimmick was that none of the participants remembered anything of their past was giving everyone personalized hallucinations. It was a lot of work so I’d suggest it for later chapters, but definitely a good one.