Neville could be the unexpected hero. He's often underestimated, but in this case, he might remember some knowledge from his Herbology studies that could help in reversing Hermione's petrification. He could find a rare plant that has the power to break the curse.
Peeves the poltergeist could be the unexpected hero. He could overhear some important information from the bad guys who petrified Hermione. Then, in his own mischievous way, he could lead Harry, Ron and the others to the solution. For example, he could start making a ruckus near the place where the cure for the petrification is hidden, drawing the attention of the protagonists.
It could be Neville. Maybe after working together in Herbology for so long, Hermione starts to notice Neville's growth and his quiet determination. His knowledge of plants might seem more appealing to her in a different light, and she might develop an unexpected crush on him.
It could be the wind. In a very different 'Three Little Pigs Twisted Story', the wind that the wolf claims to be using to blow down the houses is actually a sentient being. It realizes the wolf is wrong in trying to harm the pigs. So it turns on the wolf and blows him far away, saving the pigs. And from then on, the wind becomes a protector of the pigs, always guiding them away from danger in the forest.
A plot could be about a new student who arrives at Hogwarts just as Hermione is petrified. This new student has some special knowledge or ability related to the petrification curse. They team up with Harry and Ron to figure out how to save Hermione and also discover that the new student has a connection to the one who cast the spell in the first place. Maybe they find out that the new student's family has a feud with the heir of Slytherin.
Another aspect is the emotional depth it can add. Hermione being petrified is a very emotional event in the series. Fanfiction writers can really dig into the feelings of the characters, especially Harry. They can create scenarios where Harry blames himself or where he becomes more protective of Hermione after she is cured, which can be really interesting for readers who want more emotional exploration.
The postman could be an unexpected hero. Imagine he's been delivering mail all over the city and has unknowingly witnessed some strange activities related to Thanos' minions. One day, he stumbles upon a piece of alien technology that gives him the power to disrupt Thanos' communication network, which turns out to be a vital part of the Avengers' victory.
It could be Luna Lovegood. She has a unique perspective on magic. In the final battle fanfiction, she might use her strange but effective magical items and her unorthodox thinking to outwit Voldemort. For example, she could use some of her Lovegood family's special magical artifacts to create a shield or a trap for the Dark Lord.
It could be an old acquaintance that the main character hasn't seen in a long time.
One possible fanfiction could be titled 'The Petrified Duo: Harry and Hermione'. In this story, it might explore how their friends react to them being petrified. Maybe Ron is the first to discover them in that state and goes into a panic, trying to figure out how to reverse the petrification.
In the Mortal Cultivation Biography, Patriarch Petrification was an elder of Yellow Maple Valley, one of the seven great sects in Yue State. He was in the advanced stage of the completion level, and his magic treasure was a black ancient shield. The cultivation technique he cultivated was the Provenance True Devil Art. While waiting for the TV series, he could also click on the link below to read the classic original work of " The Legend of Mortal Cultivation "!
Happy could be an unexpected hero. Usually seen as a sidekick, in a fanfiction, he could suddenly discover a new form of magic. Maybe he unlocks a powerful transformation that gives him the ability to take on powerful opponents. He could use his speed and newfound strength to turn the tide in the games.