A narrative is a story, so in essence, you are to write an extension to "The Devil and Tom Walker." In order to make it descriptive, use as much imagery as possible, focusing on the horror and gloom of the narrative. Imagery is descriptive language that appeals to the senses, and Washington Irving used this literary element throughout his story. Also, Irving wrote the story in third-person omniscient point of view, where the reader can see how all characters are feeling and what they are thinking. Accordingly, you should follow his example when writing your narrative.
The story ends with the devil riding to Tom's house on a black horse to collect what was promised to him and dashing down the streets with Tom in his nightgown. The town sees a lightening bolt come from the direction of the swamp, and they never hear from the old miser again. Start from here. What happened once Tom and Old Scratch reached the swamp? How did the devil collect Tom's soul? What dialogue took place between the devil and Tom. Did Tom go to Hell? What happened there? Did Tom make another deal with the devil?
Use your imagination and what you know about the story to write your own narrative. Make use of any opportunity to add detail by using imagery.