In creating the boggart, Mrs. Rowling seems to have lifted a word out of Celtic mythology,1 only to then entirely disregard the backstory that mythology would normally imply.
Level of Intelligence
Like the Dementor, this is fairly debatable. Mrs. Rowling tells us of several boggarts that have taken on the shape of humans for fairly long durations.2 What she does not tell us is enough detail to know if these boggarts could pass a “Turing Test”.
Analysis
Unlike the Dementors, there are no obvious inconsistencies with the boggarts. That is not to say there are no concerns. These particular non-beings exemplify the problems with the balance of power more clearly than, I think, anything else in the books do. They can become anything, including having a reasonably effective facsimile of that something’s magic (thus it can become a Dementor. Even if it is a somewhat weakened facsimile, the fact that it can resurrect a suppressed memory and cause Harry to faint means that it is still a frighteningly over-powered creature.
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Wikipedia “https://en.wikipedia.org/wiki/Boggart” Last Edited: 2021-10-04.
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Mrs. J. K. Rowling. “Boggart” Publication Date: 2012-12-20. Last Viewed: 2021-10-21.
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