#pyrites

Ghost plots are aspects of a story that are altered or omitted from a book before it is printed. The author used the term "ghost plots" for stories that have never been mentioned or published in any Harry Potter book to date. Rowling indicated that ghost plots tended to be "superfluous to the requirements" and "had to be sacrificed for the sake of the larger story." Thus, ghost plots tended to be more peripheral or tangential to the story, making them a hindrance to a tighter, more focused plot. Sometimes, Rowling originally had two characters play the same role, making one of them redundant. Some ghost plots were removed fairly early in the writing process, while others were removed later (as indicated when Rowling accidentally provided details about ghost plots in response to fan questions). It's possible that some of what appear to be red herrings were remnants of ghost plots removed later in the writing process. Known Ghost Plots These are the main ones I've been able to find, and they could be great inspiration for FF writers or HC writers:

Dean Thomas's Father: Rowling originally planned for Dean Thomas to discover that his biological father was a wizard, left, and was killed by Death Eaters. In Harry Potter and the Deathly Hallows, Dean mentions that his biological father left when he was young and that he doesn't know whether his father was a Muggle or a wizard. Rowling has said she sacrificed Dean's backstory for Neville's, even though what we know of Neville's backstory seems to have been known to Neville from the beginning. (This may actually be canon-compliant because it doesn't conflict with anything we know from canon; it's just not explicitly stated.)

Godric's Hollow and Pyrites in the opening chapter. Rowling changed the opening chapter of Harry Potter and the Philosopher's Stone several times. She began with James and Lily hiding with Harry on a remote island instead of in Godric's Hollow. Hermione Granger's father witnessed their murder from the mainland and came out to see what had happened. She then abandoned that idea and wrote a chapter in which the reader saw Voldemort enter Godric's Hollow. In an early draft, they were betrayed by a Muggle rather than Peter Pettigrew. Furthermore, in an early draft, a Death Eater named Pyrites accompanied Voldemort to the Potters and confronted Sirius Black in front of the Potter house. Although he never appeared throughout the entire saga, some fans consider him canon, or rather, canon-compliant even if not explicitly stated. It is unknown whether Pyrites was one of Voldemort's unnamed Death Eaters during the Second Wizarding War or whether he was completely replaced as a character.

Mafalda the Weasley Cousin: Mafalda (born circa 1983) was a witch who attended Hogwarts School in the 1990s. She was the daughter of Molly Weasley's second cousin (most likely a Squib), who worked as an accountant, and a Muggle mother. Although her father was most likely a Squib, he never expected to become the parent of a witch. Mafalda began attending Hogwarts School of Witchcraft and Wizardry on September 1, 1994, and was sorted into Slytherin house. Mafalda was originally intended to compete with Hermione in academic achievement. Mafalda was a rather unpleasant individual, even to her parents. She enjoyed impressing others and showing off as much as possible (this may also have been the reason for her academic enthusiasm). She was also very nosy, frequently eavesdropping (though this included breaking the rules), and was also very talkative, prone to gossip. There are notable parallels between Mafalda's nature and that of Hermione Granger (in their academic prowess) and Rita Skeeter (in their morbid curiosities), and it is largely for this last reason that the author decided to cut this character in favor of Rita Skeeter. It would have been interesting to see a Weasley in Slytherin, however, especially since her role in the plot would have been to eavesdrop on conversations held among the Death Eater children in her house, then repeat what she had overheard to the Trio in an attempt to impress them. Hermione would have discovered that, much to her horror, Mafalda was her equal in many ways, and would have been torn between her hatred of Mafalda's disregard for the rules and her desire to try to surpass her. However, Rowling found that Mafalda "wasn't doing the job she was supposed to do," as there were severe limitations on how much information an eleven-year-old stuck at Hogwarts could gather, and consequently further developed Rita Skeeter to fill her role. So is Malfalda canon? Short answer: No. But could it be believable to include her in some FF? Yes, you can certainly use her, especially since since she would have been the daughter of a Molly wall, her actual last name wouldn't have been Weasley, which would have made headlines, but instead Prewett, Molly's last name. It's true that the book doesn't explicitly state that there's a Slytherin girl named Mafalda Prewett, but if you like the idea, you can certainly use her in your FF. I like to imagine her there at Hogwarts even if the story doesn't mention her.

Hermione's younger sister: Hermione originally had a younger Muggle sister, whom Rowling never got around to introducing, having decided it was too late to introduce her when five books had passed without her being mentioned. It would have been interesting to have a parallel with the Evans sisters. Like Mafalda, Hermione's sister is never mentioned in the last book; it's said that Hermione sends her parents away without mentioning her sister. This is up to you to interpret; let's say to be 100% sure, you'd have to say she's non-canon, but you could somehow make her canon-compliant. I'd love to read something about her.

Rowling originally created a subplot that was supposed to be in the second or fourth book, in which Nott Snr and his son visited Malfoy Manor. He and Lucius Malfoy were supposed to discuss their shady dealings in private while their sons conversed in the gardens. This scene would have shown Draco Malfoy in a different light, because he would have treated Theodore Nott as his equal. Rowling also stated that the Notts were just as pure-blooded as the Malfoys. This moment, although not shown, can be considered canon compliant and should be included in the Missing Moments.

The disastrous double date with Lily Evans, James Potter, Petunia Evans, and Vernon Dursley in late 1977. When Vernon tried to impress James with his car, the wizard in turn boasted about his material wealth, and an argument ensued. The evening ended with Vernon and Petunia storming out of the restaurant, Lily in tears. James, embarrassed, promised he would make things right, but due to their untimely deaths, he wouldn't be able to make it in time. (As before, this moment, although not shown for obvious chronology reasons, is canon compliant and should be included in the Missing Moments.)

In an early draft, the person visiting Bode at St. Mungo's on Christmas Eve was Death Eater Macnair. This is actually a small detail that could be there even if it's not explicitly stated.

During the Battle of Hogwarts, some Slytherins followed Slughorn back to join the battle against the Death Eaters. This information is canonical, the author revealed it in an interview on Pottercast 131 it is also evident from the comment that Nigellus makes at the end of the battle, in which he says that the Slytherins also did their part. The Slytherins went back to fight Voldemort and the Death Eaters. It takes courage to fight enemies and even more to fight friends and relatives

The following are early ideas that didn't make it into the final version of the books and are in direct conflict with canon:

Arthur Weasley's death: The family dynamics would have changed, and the actions and words attributed to Arthur in later books would have been portrayed by someone else, had Rowling continued with her original plan to kill Arthur.

Florian Fortescue: Rowling admits that Florean's presence in Harry Potter and the Prisoner of Azkaban was originally intended to create a subplot in which Harry later turns to Florean for information in Harry Potter and the Deathly Hallows. However, Rowling later decided to use Phineas Nigellus Black and Helena Ravenclaw to convey this information.

An alternate scene in Harry Potter and the Philosopher's Stone where the trio discuss the stone contains some interesting small changes that would have changed some of the subplots. Ron insinuates that Harry's parents stole the stone from Flamel, since in this early version it's in his vault at Gringotts. HERE and the trascription is HERE

One of the latest I discovered concerns another very early draft of Harry Potter and the Philosopher's Stone, in which Hagrid goes to speak with the Muggle minister (whose name is Fudge, obviously confusing the canonical one we know) and informs him of Voldemort's movements. There are the author's firstversions, and I'll leave them HERE and HERE. I'm also working on a transcript that I'll publish soon and add to this post. In this version, we finally find Vernon Durlsey, who here isn't just any Muggle citizen but is instead already aware of the wizarding world and seems to aspire to Fudge's position. Pretty funny. As is the vague description of Voldemort as a small man with red eyes xD

Another alternate scene from Chapter 17 of "The Philosopher's Stone" shows small changes in the dialogue between Harry and Quirrell. HERE

In the original draft of Harry Potter and the Chamber of Secrets, the Ford Anglia crashed into the Black Lake instead of the Whomping Willow, and Harry and Ron encountered the mermaids who live there. There's also a handwritten copy of this scene, which I'm leaving HERE, and I'm working on the transcription of that as well.

And now we come to the Erased characters (or never appeared):

Two other names were also considered for the Defense Against the Dark Arts teacher in fifth year: Mylor Silvanus and Oakden Hobday in place of Umbridge.

Professor Trocar, a subjectless vampire teacher, appeared on one of J.K. Rowling’s earliest lists of Hogwarts staff. A rather clever name for a vampire, a trocar is by definition a sharply pointed shaft inserted into arteries or cavities to extract bodily fluids. Trocar disappears fairly early on in her notes, and despite fan rumors labeling Snape a vampire, Rowling confirms that he is not a revamped Trocar.

Enid Pettigrew was considered for two different subjects: as a possible Defense Against the Dark Arts teacher in the fourth book or as a Divination teacher. Ultimately, the roles went to Alastor Moody and Sybill Trelawney, respectively.

Professor Mopsus was originally planned to be the Divination teacher in Harry Potter and the Prisoner of Azkaban.

Aurelia Sinistra In a handwritten planning note, Professor Aurora Sinistra was recorded as "Aurelia Sinistra." The name Sinistra also appears next to the list of Defense Against the Dark Arts professors, but it's very likely that this is just a simple name change and actually refers to our dear, canonical Aurora Sinistra.

Muggle minister As mentioned above, in an early draft of the first book, when Hagrid goes to speak to the Muggle minister, he's named Fudge. This scene was adapted into the sixth book, but this Muggle minister was actually replaced.

Angus McKinnon and Elspeth McKinnon, also in the same chapter above, are named as two members of the McKinnon family who we're told were personally kidnapped by Voldemort because he wanted them on his side. It's unclear whether these two characters were merged into Malerlene or whether they still exist in the canon, simply not explicitly stated. I lean more toward the latter, given that in the first book we're told that the McKinnon family was attacked, thus implying more people from early drafts of Harry Potter and the Philosopher's Stone

And of course, the aforementioned:

Pyrites (Death Eather)

Hermione's sister