Now, its a common trope, but one with a lot of potential, to have your culture bathe in urban legends, a natural product of civilization, and have the plot be spurred into motion by the sudden realization that, oh no, this creature and other world they believed in half in jest was actually real. Unfortunately, as I said, its a very common trope, and it'd likely induce some eye-rolls for one to sit through unnecessary amounts of time dumping details into the urban legend so it has a basis for the narrative, which often gives away the urban legend is real anyhow and then, lo and behold, something happens and the characters learn the mythological creature is real. How would I be able to present an urban legend in my world and have it, say, have a slight degree of validity without relying on the typical contrived means of executing this plot point?
I guess it would depend on which urban legend is occurring in which world. I can't say I'm familiar with anything similar to this, so I wouldn't know which tropes/cliches to avoid.
Well if you want a "This just became actually real" deal then you could have someone the character knows die from mysterious circumstances via the urban legend and have it unroll like that. But, my opinion, if you want it more real I would suggest having it real to start out with. Having them know it does exist but be less a part of their lives and introduce it as more of a problem to them as the story goes on.
Well, it would be real to begin with, of course, but, if I may clarify without coming off as rude, they basically believed the urban legends half in jest. Part of them and most "reasonable" people consider the stories silly falsehoods. It just turns out it HAD actually been true in the past. But I do like and would consider having some strange, inexplicable occurrence (such as someone's death) as a means to introduce the validity of this urban legend.
If you build it on something people recognize, an urban legend or myth that already exists IRL, or let it contain aspects from everyday life IRL, it will be easier to believe and require less explaination.
Maybe start the story with acceptance of the fact that the urban legend is true, then work back e.g. through flashbacks, to a time when people thought it was only a myth. You can show how the myth came from the creature, not the other way around. Have you ever seen the documentary Cropsey? It is a really good example of this. I understand that if the shock factor of it being real is important then it won't work, but if you're worried that it will be obvious anyway then you might as well subvert the cliche a bit by just acknowledging it outright.
You could begin with your characters believing that the legend is real, because of what they have been told all their life. that way, you could use that "certitude" to explain and develop what needs to be explained in order to be coherent later on. Your story would begin with your MC absolutely certain that the legend is true. Then, as he/she becomes more and more worldly, interactions with other people and their beliefs show him that he might have been wrong and lowers the certitude level. You could create "proofs" that the legend is childishly naive. Then, when you want the legend to be proved, by whatever means you choose, you can create some kind of surprise, since you'd have conditioned the reader to expect something more rational to happen.
I have been bouncing an idea around about someone investing the origins of urban legend only to find it grounded in fact. And there are people about who do not want these facts brought to light.
I love stories based on urban legends and creepypasta. But I don't really understand your post @isaac223 so I can't help...