Ultimate Plot Hole That Forced JK Rowling to Completely Rewrite Goblet of Fire
If you were paying very close attention (and/or have a perfect memory), you may recall Ron Weasley offhandedly mentioning that his mother has a Squib cousin.
If you were paying EXTREMELY close attention you would have learned that behind the scenes, this part of Ron's family history nearly had a big impact on the Harry Potter universe.
Mafalda Weasley was supposed to be the child of Molly's Squib cousin and a Muggle, born with magical powers against all odds. Originally, JK Rowling intended Mafalda to appear in Harry Potter and The Goblet of Fire as a sort of Slytherin foil for Hermione: ambitious, fiercely intelligent, and academically competitive.
According to Rowling, Mafalda was going to be a "highly-strung" and "very gifted" young witch who was prone to eavesdropping and gossip.
She would have spent her time listening in on conversations between Death Eater parents and their Slytherin children, and her pleasure in delivering bad news would have simultaneously harmed Harry's reputation and occasionally given the Golden Trio scraps of useful information.
It was Mafalda who was originally meant to spread nasty gossip in The Goblet of Fire, including the rumors of Harry's instability and Hagrid's background. This gossip would grow to seriously damaging proportions in later books.
So, why did Rowling make the decision to scrap Mafalda's character? According to the author, Mafalda left the book with a major plot hole. Just how was a young student able to so radically influence the outside world's opinion of Harry, to the point where the Ministry for Magic grew to distrust him?
Rowling ended up deleting Mafalda and creating Rita Skeeter, a journalist for "The Daily Prophet". With Rita, Rowling was able to create a character with enough influence over the wizarding world that her impact on Harry's reputation made much more sense.
Rowling later said that she was glad she covered up the plot holes created by Mafalda, even though doing so caused The Goblet of Fire to come in months behind schedule.
While Mafalda Weasley may not have made it into the Harry Potter series, her character is an interesting example of how even the most well-planned characters may not make it into the final product. Rowling's decision to replace Mafalda with Rita Skeeter ultimately allowed her to explore some different themes and to create a more dynamic character that added to the richness of the Harry Potter series.