What are the moods in the story, "The Devil and Tom Walker"? How does Irving create humor in the story?

Even though the story is one based on a dark legend of one selling his soul to the devil for personal gain, Irving tells it with wry humor.  When Irving describes both Tom Walker and his wife, he does so with a twinkle in his eye, saying, "...they were so miserly that they even conspired to cheat each other." Neither husband nor wife seem to have any fear of the devil because they are both too consumed with greed. Tom's wife sets off to find the devil and make her own pact because Tom doesn't want to give his wife the satisfaction and possible benefit from him selling his soul and so threatens not to go through with the deal.  When she doesn't return, Tom eventually goes in search of her - not because this is his wife who is missing and he misses her, but because when she left, she took some valuable household items with her and Tom wants them back.  Tom finds his wife's apron with only a heart and a liver in it.  So, the reader is told, "Tom consoled himself for the loss of his property, with the loss of his wife, for he was a man of fortitude. He even felt something like gratitude toward the black woodsman, who, he considered, had done him a kindness."  The humor is as unmistakeable as it is old.  The same sense of humor survives to the end of the story when, Tom, now rich from charging outrageous interest rates in his money-lending business, says in anger, "The devil take me if I have made a farthing!"  The devil then takes Tom.