Not playing at conventions, but conventions I’ve adopted in my games (mostly regardless of system or genre) to try to shape the play experience to encourage or avoid certain kinds of play at my table. These aren’t house-rules, most of them being meta-rules about what is and isn’t allowed by the GM or the players. Also most of these are guidelines, and might be relaxed on certain occasions or if everybody is agreeable.
- No Player-vs-Player action. No attacking other PCs, no stealing from them, no actual intra-party conflict. “Pretend” intra-party conflict, where the players roleplay that their characters are squabbling like Legolas and Gimli, but pull together as a team when the action starts, is fine. But if tempers start to rise, I cut it off. There are a lot of players and groups where this kind of stuff is meat-and-potatoes to them, but I’ve been burned too many times by what’s started out as a bit of fun and escalated until it ruined the game for everybody, so I take a hard line on it now.
- No Torture. Torture is something evil NPCs do off-screen to other NPCs, or a player might have as something that happened to their character as part of their back-story, but it never gets any play time. As a corollary, captured NPCs will always spill their guts to the PCs at the slightest encouragement; they may not know much, but I explicitly promise to the players that as GM I will never create a situation where they would be better off torturing a captive for the information they need regardless of how plausible they might find that in real life.
- No Using PC’s Attachments Against Them. Unless the player volunteers for it, I promise as GM that if they form bonds or connections with various NPCs and locales, I’m not going to use that for cheap drama or as a way for an NPC villain to compel their cooperation. Yes, that cuts off a bunch of seemingly interesting stories and scenarios, but you know what also cuts off a bunch of interesting RP? Players refusing to form any bonds or connections with any of the setting for fear of having it held hostage or weaponized against them.1
- Mercy Works. There’s a thing that some GMs like to do (and I admit I’ve done sometimes in the past) where if you let a bad-guy get away, it’ll come back to haunt you. It’s tempting because recurring villains are a staple of a lot of genre fiction, and the players having a back-story with the villain can be so satisfying, particularly when the players come to really hate the villain. He shows up again and they’re automatically invested. The same thing can happen with un-named mob monsters or bandits, where if you don’t kill them when you have the chance, they’ll just bother you another day. The problem is that players are usually very rational, and very ruthless, so unless you’re enforcing genre conventions that forbid it (e.g. codes against killing in super-hero games) the players learn to leave no living enemies… but that can really mess up the tone of the game, and I think contributes to murder-hoboism. It’s also relatively unrealistic, at least if you go by the history of warfare in our world. There were lots of reasons historically to take captives and not kill them, or to let fleeing soldiers get away, if for no other reason than it stiffens the resolve of the enemy to die rather than be captured but the structure of a lot of games (especially dungeon crawls) makes that difficult to implement. My solution to keep my players from committing war-crimes (or at least reduce their number) is to have the players’ intelligent foes be permanently defeated: if the players show mercy, they will never again oppose them (whether from fear or gratitude) and if the players are generous they might change their allegiance. They explicitly will not be constantly searching for ways to backstab the players.
This one is a bit more squishy than the others, because it really depends on what it means to defeat the enemy. If they fail a morale check and rout, then yeah, they might regroup and be a problem later. What I’m really trying to prevent is pushing the players into feeling they have to slaughter helpless captives or go around the battle-field applying a coup de grâce against anybody who might merely be injured or unconscious.
- Surrender is an Option. Bad-guys in my games will usually accept surrender, and it doesn’t mean the end of the PC who surrenders. Even for unintelligent monsters I might think about whether it would drag the victim back to its lair to eat later or something. There will usually be consequences, a ransom to be paid, or they’ll have to escape, but I try not to ruin the character for acting reasonably in the face of overwhelming force. At the very least I’d prefer that Death before Surrender! be a choice that says something about the character and not, well the GM is going to kill my character anyway so might as well go down fighting.
- Naturally there are exceptions for game/genres where it’s an explicit part of the game; if you’re playing a super-hero game with the concept of a “Dependent NPC” like Aunt Mae who will get into trouble as a complication for the PCs heroic guise, then something happening like her getting engaged to Doc Ock is still on the table.