Hi hello, what the heck is narratomancy pls and thx
 ohohoho I will gladly tell you
In short, narratomancy is the semi-canonical magic/logic/physical law the Mechs universe operates under. That law is basically “whatever is best for the story is what happens.” This is why Jonny is dead for about a minute in How the Aurora Was Won, dead long enough for Brian to have to babysit his corpse for Gender Rebels, and also barely flinches during Sleeping Beauty– all those stories require different things for narrative convenience. It is kind of silly from a Doyleist point of view, and very hand-wavey, but also extremely fun to play with as soon as you get over the initial ridiculousness.
The strongest canonical basis for this is this post from Jonny on the official mechs tumblr, which says that their regeneration “tends to follow a rough logic of whatever works best for the story” (which is quickly refuted by Nastya), and to my knowledge the most comprehensive source on the theory from the fan side is this meta from @gunpowderdtim. There’s also a piece of HNOC fiction on Kofi Young’s blog that brings up the concept of narrative Echoes, which ties into all this as well. I believe the term “narratomancy” was coined by @lucky-sevens (who is no longer active, but whose meta is well worth reading) to mean “story magic.”
Ultimately, like most elements of canon, it is a very loose pattern occasionally alluded to, which the fandom then took and ran with, and something that probably varies based on which member of the band you ask. It’s also an extremely useful term and tool to use when analyzing the sheer chaos that is mechs canon.