[@Mattchstick] 

This is sounding better and better! I think it could be a combination of one and two on how to insta-kill a character, depending on the player. I like the phone texting aspect of the game as it really sets the stage- as for a slow acting toxin, I don't know if that works depending on how long the game ends up lasting, especially if your doing day/night cycles. If the experiment was only one day long I'd be down for it though. I like the idea of day and night cycles except if someone doesn't post a reply during the same cycle as whatever they are situated in- it might get a bit confusing? 

All great ideas with no easy answers and I'm excited to play :)