What is the purpose of having Mistress Hibbins appear sporadically throughout the novel?

Mistress Hibbins is the resident witch. We are not sure if she was a witch in real life but Hawthorne seemed to think so anyway. Mistress Hibbins is a widow who lives with her brother, Governor Bellingham, in a luxurious mansion. I suppose being a widow was half way to becoming a witch if you were a Puritan. Apparently Mistress Hibbins goes into the forest and pals around with a "Black Man" at night. She shows up now and again to remind the already paranoid Puritans that evil is just around the corner and that they should all be double paranoid if they see their friends and neighbours petting a black cat or something.

Mistress Hibbins is a representation throughout the entire book. Hawthorne put her in the book to represent naturalism as a whole, how the naturalists have a different view that connects them to emotions more. Hence why she was so inclined that she really did know who Pearl's father was. No Hawthorne did not think she was evil, the Puritan community did. There is a strong difference because it gives the reader a sense of not only the setting but of the Puritan view on evil. Hibbins also is a representation of Pearl and what the possible outcomes are for her. If Pearl were stay dejected from society the way she had begun she would probably be made to walk the gallows as Hibbins did. The person who answered before me is entirely incorrect.