In "The Devil and Tom Walker," how does Washington Irving depict the Devil in an Americanized way?
There isn't very much information given about the Devil that helps us to specifically fit him to any particular theme or stereotype. "Americanizing" him should, by definition, involve attributing something distinctly American to his appearance, behavior or speech, such as the slang he uses or the clothes he wears.
The Devil is named "Old Scratch", which is a common folk nickname for the Devil, though generally fallen out of use in modern times. This might be considered a form of Americanization if that nickname was not used anywhere else.
Another element is his clothing; a "rude, half Indian garb", indicating that his clothing was unrefined and took significant inspiration from Native American dress, or was composed of pieces salvaged from such. Unfortunately the details are sparse, but this depiction seems to suggest that the Devil, like America, was beginning to incorporate what had surivived of the Native Americans and their culture into itself.
A third element is that the Devil is depicted with characteristics of a working man and frontiersman, American aspects that have been stereotyped since the colonies were founded. This contrasts more traditional depictions of the Devil as haughty, refined and unaffiliated with earthly jobs and titles. Despite his appearance he nevertheless has a cordial way of speaking and doing business, when it suits him, which might match up with the perspective that Americans had descended from "civilized stock" and retained some of those traits, but were now distinctly more "wild" than their European counterparts.