One of the superstitions in the article 13 Halloween Superstitions & Traditions Explained is about bats:
Medieval folklore also described bats as witches' familiars, and seeing a bat on Halloween was considered to be quite an ominous sign. One myth was that if a bat was spotted flying around one's house three times, it meant that someone in that house would soon die. Another myth was that if a bat flew into your house on Halloween, it was a sign that your house was haunted because ghosts had let the bat in.
I'm very interested in reading such tales, but my searches so far have been successful. Most search results seemed to be about bat familiars in games (e.g. Castlevania).
Could you point me to actual folklore tales that feature bats as witches' familiars?