I just noticed that we have a tag mystery. Its tag wiki excerpt rather unhelpfully says:
a mystery is something that is difficult or impossible to understand or explain. Or a novel, play, or movie dealing with a puzzling crime, esp. a murder.
without giving any clue as to how the tag is meant to be used on this site. As for current usage, at the moment the tag appears on 20 story-ID questions and 10 others. Of those 10, some seem to have the tag just because the OP is asking about something they consider a mystery - How do Horcruxes work?, Can someone explain the ending of "Enemy"? - and some simply because they're about mystery stories, e.g. Understanding the limericks in Asimov's mystery story, "Out of Sight" and What's the sequence of events Milo discovers in "The Counterfifth Detective"? The first of these usage types at least should be killed, otherwise mystery could be used on nearly every question on the site; and the second is not usually how we use genre tags here.
Should we keep this tag? If so, how should we be using it, and what should the tag wiki say?
(Note that even getting rid of the tag entirely would require at most 10 manual edits, followed by a merge into story-identification. Whatever we decide, it's not going to be a huge operation to "make it so".)