In "The Devil and Tom Walker", what are some details describing the setting that suggest something sinister and supernatural?
At several points the story includes sinister and seemingly supernatural details, almost of all of them centered around the appearance of Old Scratch.
When Tom first meets Scratch, he's been taking a shortcut through a swamp and eventually passes by an old Indian fort, which has fallen into ruin. The imagery of the fort is foreboding; we are told people know not to linger there because of the evil reputation of the place, but Tom doesn't seem to mind. He rests against a hemlock tree (one famous for being used as a method of execution by poison) and pokes at a cluster of black mold, and then happens to find a human skull with a tomahawk embedded in it. The tree, mold and skull all carry a sinister symbolism of death.
Later, when Tom's wife disappears and he goes looking for her, he finds her apron tied in a tree with a vulture near it. Vultures are also symbols of death and decay.
Finally, there is an abundance of imagery at the conclusion of the story. Scratch appears to collect Tom's soul as a thunderstorm approaches (symbolizing his supernatural power) and a lightning bolt strikes what is apparently the spot where Tom is "taken". His possessions are also destroyed or reduced to useless junk, none of which involves a literal transformation before anyone's eyes, but the coincidence of which is too much for the reader to really believe could occur naturally.