What are the fairy tale elements in "The Fall of the House of Usher"?
Well, there are certainly lots of elements in this classic Gothic story that are reminiscent of a fairy tale or a ghost story. You might want to consider the isolated location of the House of Usher, which of course adds a psychological component to the experience of the narrator as he is away from civilised society. Added to this, consider the way in which both Roderick and his twin sister Madeline are described as being half-dead and half-alive. The narrator cannot look at Roderick "with any idea of simple humanity" and likewise when he catches a glimpse of Madeline, the narrator looks at her with "an utter astonishment not unmingled with dread."
Lastly, the shocking revelation that Roderick actually buried his sister alive in the tomb combined with her ghostly reunion with her brother gives this story a real horrific fairy tale ending:
For a moment she remained trembling and reeling to and fro upon the threshold--then, with a low moaning cry, fell heavily inward upon the person of her brother, and in her violent and now final death-agonies, bore him to the floor a corpse, and a victim to the terrors he had anticipated.
The way that the fates of Roderick and Madeline are matched by the destruction of the house adds a real supernatural element to the conclusion of the story, as it becomes clear that the fates of these three were inextricably intertwined in their life and death.