Celebrim
Legend
In your own words, not using jargon or other bespoke terminology. What, to you, qualifies as a "narrative mechanic"?
This is going to be hard because I don't know what counts as jargon.
A "narrative mechanic" is when the rules for adjudicating a situation in the game depend on the narrative rather than things internal and intrinsic to the imagined situation.
That's a bit hard to wrap your head around so let me break it down and I think I'm going to need a word that might strike some as jargon and that is "metagame".
So you have three levels of participation in the act of play - the imagined scenario, the game rules themselves, and then the way you approach the game or "the metagame". The metagame is what the players are thinking about achieving by playing the game. In a competitive game this might be their strategy for the game. In a cooperative social game like a typical RPG this could be a number of things but is often, at least in part, creating an exciting story.
I'm also going to eventually need to talk about the proposition and adjudication cycle in a formal way, so let's just define that now. RPGs have rules to deal with situations where the a participant in the game proposes to do something but the outcome of that proposition is uncertain. For example, in a typical game of make believe you might have a player propose, "Bang, I shot you!" and then another player propose, "No you didn't; you missed!". In order to keep the game going, we have to have some mechanism to adjudicate between these contrasting propositions. That method could be a lot of things, the range of which aren't particularly important to know now, but for example we could play rock-paper-scissors.
A "narrative mechanic" is a game rule that essentially says, "If the action would result in creating a better story, then it should be more likely to work." So far as I know, the first example of a "narrative mechanic" was in the game of Toon, which had a rule that said simply, "If it is funny, it happens." That is to say, the rules themselves said, "If the resolution of a proposition would result in achieving the goal of the game - humor - then that proposition just succeeds." The metagame here is directly impacting the game. Players want to laugh, and therefore all other rules should get out of the way for that goal.
It's not a particularly nuanced narrative mechanic, but it is one. I point this out mainly because I don't want the lack of nuance to be the distinguishing feature here. A more nuanced version of the above would be "If what the player proposed is funny, then they gain some advantage in adjudicating the proposition that makes it more likely to succeed."
All narrative mechanics are some version of that, just with differing degrees of subtlety. In a traditional RPG, the hero triumphs over the bad guy because he's strong, powerful, and has a cunning plan. If none of those things are true, well then the hero probably doesn't triumph. But in a narative RPG, the hero triumphs over the bad guy because he's the hero. Or conversely, maybe the game isn't rigged to tell that sort of story, so maybe the hero tragically fails because everything is meaningless and then you die. Or maybe love triumphs over all. When you have narrative mechanics, the game rules themselves are rigged in favor of these story elements. The game rules are themselves aware of what the game is supposed to be about and no intrinsic explanation is really needed. If the game is about "love triumphs over all", either because the designer said so or because a participant declared so when defining what the game is about, well then, "Because my love is threatened..." gives you advantage in the proposition.
That's what a "narrative mechanic" is.