The Enemy Within
Heaps of games have one big thing in common: the player characters wind up being a team because it’s easiest to run a game if they stick together and are on the same side. Genre or not, it’s the result of the pure logistics of having people at the table.
But what if instead of introducing external antagonists you mix it up a bit and have existing player characters take turns being the antagonist? Not the player running a different character, the normal player character taking sides against the so-called party.
Each game or game arc something is introduced that at least temporarily puts one character in an adversarial roll against the other player characters. Once the arc is finished, the character goes back to being part of the team. Next time a situation arises that puts a different character in the hot seat. Each conflict could erupt into full bore combat (well, non-lethal anyway) or it could just be argument and attitude, whatever fits the genre.
One game session the player character team is supposed to survey an ancient burial ground, but one of the characters starts to feel her roots and tries to stop the other characters from violating the sacred land. She might just argue or actually run off into the woods and sabotage the team’s equipment. Either way, she’s the enemy for the moment.
The trick would be to make sure that the conflict was set up in such a way that the other players didn’t just side with the opposition player. It might just be part of the gentlemen’s agreement of the game: when the opposition player takes a side, you angle for opposing them, not sympathizing with them. Or you could include a practical plot reason that made opposing the rogue character urgent and vital:
The team is surveying the terrain because there are risks of landslides that could endanger a nearby town. They need to get their job done or real live people will be in danger — no more jibba jabba about ancient spirits!
You would also need to leave the door open for resolution and renewed solidarity. Does the opposition PC recognize the error of their ways? Does the situation just change so the issue is moot? If the opposition PC took a stance that the other players could respect even if they didn’t agree (some kind of moral or ethical stance) than a reconciliation isn’t too hard once the immediate pressures are removed. If not, the opposition PC would have to completely about face and basically apologize for the error of her ways — either works.
There are also secondary effects, like putting each character in the spotlight when they are the opposition, and pushing more roleplaying since the players are spending more time talking (that is, arguing) among themselves instead of yelling at NPC adversaries.
I know what you’re thinking: was this idea really inspired by Gareth Marenghi’s Darkplace? All I can say is, “Let’s do this!” Sure it works in a surreal sci-fi/horror comedy, but it could work just as well in a realistic setting if you were careful to pick good conflict plots.