What are the elements of dark romanticism, implemented by the author, in "The Monkey's Paw"?

Dark romanticism was a literary offshoot of the 19th century philosophy of Transcendentalism. Dark romantics believed the Transcendentalism of Emerson and Thoreau was way too optimistic about life and the individual. Whereas Transcendentalism focuses on the divine spirit of the individual, dark romanticism allows for evil to be a disruptive force in a person's life. Dark romantic writers included elements of the supernatural into their fiction, including devils, ghosts, vampires and, in W.W. Jacobs' "The Monkey's Paw," an evil talisman. Dark romantic stories included supernatural elements, horror and madness. 

Dark romantics concentrated on human fallibility and the tendency toward sin. People are often tempted by the supernatural, just as Faust is tempted by the devil in Goethe's famous tale. In "The Monkey's Paw," the Whites, particularly Mr. White, is drawn to the paw. The Sergeant-Major has explicitly expressed the evil of the paw by telling the Whites that the first man had two wishes and with the third he wished for death. Despite the warnings, Mr. White takes the paw and makes his first wish. It seems like quite an innocuous request. He only wants a small amount of money to pay off his house. Of course, the paw is evil and the request will not come without horror.

The first bit of horror is described just before the end of Part I when Herbert is alone. He sees horrible images in the fire:

Herbert sat alone in the darkness, gazing at the dying fire, and seeing faces in it. The last face was so horrible and so simian that he gazed at it in amazement. It got so vivid that, with a little uneasy laugh, he felt on the table for a glass containing a little water to throw over it. His hand grasped the monkey's paw, and with a little shiver he wiped his hand on his coat and went up to bed.

The next day, Herbert ends up dead and Mr. White is presented with the money he had wished for. It is then that madness enters through the form of the overwhelming grief Mrs. White feels for the loss of her son. She pleads with her husband to "wish our boy alive again." Mr. White is afraid of what might happen if he makes such a wish. His son had been badly maimed in an accident and has been buried for ten days. He tells his wife,

"He has been dead ten days, and besides he—I would not tell you else, but—I could only recognize him by his clothing. If he was terrible for you to see then, how now?"

Nevertheless, Mr. White wishes Herbert alive again and Jacobs builds suspense as they wait for the hideous corpse to walk the two miles from the cemetery. When the knock at the door comes, Mr. White comes to his senses and despite the protestations of his wife, uses his last wish to get rid of the monster that was once his son.

Thus, the supernatural, elements of horror, and madness brought on by despair are chief aspects of Jacobs' macabre story. For these reasons it can be considered an example of dark romanticism.