This is a problem as old as the game: How does a DM get the players to stop just outright slaying all NPCs, but more specifically the "good guys". Assuming that the PCs are at least sort of good, or at least want open access to good/neutral civilization.
This is not a problem in my Hard Fun Old School Unfair Unbalance style games. So here is what happened over the weekend:
Another DM could not make it to his game, so he asked me to cover for him. He gave me his notes, but we had no time to chat. So it's an urban set game, I'm not sure it it's published or homebrew as I only had his notes. Last game the PCs did a task for an NPC, and the game ended at a big party. This game picks up at the party. The players have fun for a bit and then the plot kicks off: the NPC is found murdered...and the PCs get blamed for it. The PCs surrender and get taken to jail. They get informed that they will spend the night in jail as the judge won't be in until morning. The players panic a bit here and try to escape...but fail. As per the plot, later that night a shadowy figure shows up and offers to free the PCs if they do a job for him. The PCs agree to this magically bound quest. While the PCs could have made a quiet escape....they don't. The guards get alerted and alarms are sounded.
And as the city guards attempt to recapture the escaping prisoner PCs, the PCs just go full blown murderhobo on all the city guards. So this is the good city where a lot of the rest of the game is set, going by the notes. And the PCs getting arrested for falsely killing the NPC, that they could have been found innocent for, does not even matter now. The PCs have now just become the worst mass murderers in city history killing many guards and such.
The players never give any of this role playing any thought. They are LOCKED into the idea that ANY combat encounter MUST be a murderhobo slaughter fest to the death. A guard hits them with a net, they must use thier most deadly weapons, spells and abilities to do a ton of damage and slaughter the guard.
After the slaughter fest, the PCs flee the city and go to hide in some caves. And this ends the adventure for the night. Of course, next game brings up the problem: what will the city do about the most vile and evil mass murderers in all of history. Sure you could just ignore it. But most DMs like to have a bit more 'reality based games' where consequences matter.
I sent the game notes to the games DM, and he was a bit shocked the players did the murderfest. There is a chance, he said, he might need me to cover the game next week. So that puts it back to me of what might happen. My reaction would be the super harsh way...killing the characters. And maybe reseting the game with some time travel or something like that.
But this leaves the issue of talking to the players. I'm not really a fan of talking. They think they did nothing wrong by slaughtering so many NPCs, but then still "get" that they had to flee the city as they are now mass murderers. I know from many past "talks" that nothing much will come from such a talk. I'm sure the players will say "anything in the game that gets in my characters way will be slaughtered!!!!!!", as that is exactly what they did.
But....here I am. Asking for maybe another view point? Is there anything new to say on this topic? I guess someone might say that a game must have a session zero where the DM very slowly and carefully tells the players the way good, evil, slaughter and common sense work in the game. Though in this case it's not "my" game. Still the players "get" that it was wrong to slaughter all the guards......but that did NOTHING to stop them.
So, anyone?