In a 'harry saves everyone fanfic', one key plot point could be Harry discovering a new, hidden power within himself. This power might be the key to saving everyone. He could also form new alliances with unlikely characters. For example, he might team up with some Slytherins who have a change of heart. Another aspect could be that the situation is extremely dire, like the whole wizarding world is on the verge of destruction. Harry then has to go on a quest to find ancient magic or artifacts that can turn the tide and save all the wizards and witches from harm.
It's likely that in this 'harry saves everyone fanfic', Harry has to overcome some personal struggles first. He might be doubting himself after a series of setbacks. However, he gets inspired by the memories of his parents or Dumbledore. Then, he starts to formulate a plan. He might have to travel to different magical places, like the Forbidden Forest or the Chamber of Secrets. There, he could encounter various magical creatures that either help or hinder him. Eventually, he uses his skills, knowledge, and the help he's gathered to defeat the threat and save everyone in the wizarding community.
One key plot point could be Naruto facing a new and powerful enemy that no one in the village can defeat alone. He might have to master a new jutsu in a very short time. For example, he could discover a secret about his family's past that gives him an edge. Another plot point could be Naruto uniting the different clans in the village. Since they all have different abilities and grudges, Naruto would need to use his charisma and leadership to bring them together to fight the common foe.
In some versions of 'harry becomes an obscurus fanfic', the key plot could be Harry's journey to master the Obscurus power. He might start out as an outcast because of it, but then discovers that it can be a weapon against the real threats in the wizarding world. His relationship with Dumbledore or other authority figures might change as they try to help or restrain him. And there could be a big showdown where he has to decide whether to fully embrace or reject the Obscurus within.
A common plot point is Tonks arriving just in time. For example, Harry might be surrounded by Death Eaters, and Tonks shows up out of nowhere, using her combat skills and magic to fend them off. Another is Tonks using her Metamorphmagus ability to deceive the enemy. She could transform into a Death Eater to get close to Harry when he's held captive. Also, often Tonks has to overcome some sort of obstacle or enemy plan before she can save Harry, like breaking through a magical barrier that was set up to keep her away from Harry.
Obviously, Harry Potter would be the main character. He is the one doing the saving. Ron Weasley and Hermione Granger are also likely to be main characters as they are Harry's closest friends and often by his side in his adventures. Dumbledore might also play an important role, even if he's dead in the original story, his influence could still be there guiding Harry. And of course, there would probably be villains, perhaps Voldemort or some new dark wizard created for this fanfic.
One common plot point is that Percy discovers Calypso is in some sort of peril, like being trapped on an island or held captive by a powerful enemy.
Well, one key point could be the moment Raven decides to save Ruby. Maybe it's because she sees some untapped potential in Ruby or perhaps a sense of family she can't deny. Another point might be the challenges they face during the rescue. It could involve fighting off Grimm or other foes. And finally, there could be an emotional moment between them after the save, where they start to understand each other better.
One possible plot point could be Dudley finally realizing the true nature of the danger Harry is in and using his new - found courage to save him. Maybe he discovers some secret about Voldemort that helps him protect Harry. Another could be Dudley using his physical strength, which he was known for in the original series in a more heroic way to fend off Death Eaters.
In this fanfiction, perhaps the old Team 7 is framed for a crime they didn't commit. Naruto takes it upon himself to clear their names. He starts by investigating the real culprits, which leads him into the underbelly of the ninja world. Along the way, he discovers secrets about the past that could change the way they all view each other. He might find out something about Kakashi's past missions that were related to the current situation. Sasuke and Sakura could be in hiding, but Naruto convinces them to come out and help him prove their innocence. The story could end with Team 7 being exonerated and their reputation restored.
In a 'Marge Saves Harry' fanfic, the plot could start with Harry ending up in Springfield for some reason. Marge discovers him and his magical abilities. When she learns of the threats he faces in his own world, she decides to accompany him back to the wizarding world. Once there, Marge uses her homemaking skills in a creative way. For instance, she could use her cooking skills to make potions or her knitting skills to create magical items that help Harry in his fight against evil. Along the way, there would be a lot of cultural clashes between the Muggle - like Springfield values and the wizarding world's traditions, which would add an interesting dynamic to the story.
The plot might start with Snape realizing that Harry is in need of a proper family. So he decides to adopt him. As the story progresses, they would need to adjust to living together. Snape would have to change his living quarters to accommodate Harry. There could be a lot of emotional moments like when Snape tells Harry stories about his mother. Also, the fanfic could explore how Snape helps Harry deal with his fame in a different way than the Dursleys did. He could teach Harry to be more humble and use his fame for good in the wizarding community.