Ghost of the Mirror (1974)

To help his ailing mother, an un-named young man agrees to copy the Buddhist scriptures in a quiet place, bathe regularly, and avoid the company of beautiful women. With his slave boy, Ching, he goes to live at an abandoned estate believed to have a haunted well. Though he disbelieves at first, he discovers it is haunted by Su-Su, a ghost of a drowned girl merged with an enchated mirror spirit called Yau Ying. She is forced by a poisoned dragon to kill bad people, but claims that he is too righteous for her to harm, despite some ectoplasm-infected attempts to strangle him with her sash. She agrees to be his servant for shielding her from the dragon, and gives him the peace required for him to do his transcription, even receiving the approval of his mother. Ultimately, they are forced to confront the dragon.