Well, it could be Neville Longbottom. He was often seen as a bit of an underdog in the original series, and in a 'Stupid Wizards' fanfic, he could be the one to show that the so - called stupid wizards have hidden strengths. For instance, his knowledge of herbology could be used in a really unique and unexpected way.
Crabbe and Goyle might also be prominent. They were not exactly the brightest in the original books. In this type of fanfic, they could be given a chance to shine in their own way. Maybe they accidentally discover a powerful magic because of their clumsy and 'stupid' actions.
Obviously, Harry Potter himself would be a central character. Ron and Hermione, his closest friends, would also likely be in it. Ginny, as Harry's love interest, would probably play a significant role too. Other characters like Neville, who has grown into a strong wizard, could also be featured. And of course, we might see some of the old Hogwarts professors, perhaps McGonagall still guiding the school in some way.
Obviously, Harry Potter himself would be a central character. He's the main protagonist in the series, so it's likely he'd be involved in the Christmas - related events. Hermione Granger would also be there as she's Harry's best friend and loves to participate in all things magical and festive. Ron Weasley too, as he's part of the trio. Dumbledore might also make an appearance, perhaps guiding the students in some Christmas - themed activities or sharing some wise words about the season.
One common theme could be the subversion of the traditional wizarding hierarchy. In some 'Harry Potter' fanfics with a 'Stupid Wizards' concept, the characters might question and challenge the established authority of the Ministry of Magic or Hogwarts professors. For example, they could expose flaws in the way magic is taught or the laws that govern the wizarding world.
Well, for sure Harry Potter is a top pick. His connection to Gringotts started early on when he first visited to get his inheritance. Hermione would be there as she's the brains of the group and would be curious about any magical lore associated with Gringotts. Ron, with his family's financial struggles, could also play an important role. The goblin bankers are a given as they are the heart of Gringotts. In terms of crossover characters, if it was a crossover with 'Alice in Wonderland', the Cheshire Cat could make an appearance. It could be lured by the shiny objects in Gringotts and cause some chaos as it tries to steal something, with Harry and his friends having to stop it.
In 'harry potter is betrayed fanfic', Luna Lovegood might be a character who betrays Harry. Maybe she is under the control of some mind - altering spell or has been deceived by a false prophecy that makes her think she is doing the right thing by betraying him. Also, Hagrid could be a shock betrayer if he is somehow forced to choose between Harry and his beloved magical creatures, and chooses the latter in a way that is seen as a betrayal to Harry.
Even Ginny could be written as a betrayer in a fanfic. For example, if she becomes possessed by a dark force, she might turn against Harry. Her relationship with Harry is so central in the original story that a betrayal from her would be a huge shock and create a lot of drama in the fanfic.
Harry Potter himself could be a main character. He has a history of standing up against injustice, so it's likely he'd be involved in a revolt. Hermione would also be a key figure. Her intelligence and knowledge of the wizarding world's laws would be invaluable in planning and leading a revolt. Ron, with his loyalty and courage, would be right there with them.
Harry Potter would probably be one of the main characters. He's the central figure in the original series, so it's likely he'd be involved in this fanfic in some capacity, perhaps as the hitman or someone related to the hitman - style plot.
Well, Ron is also a candidate. He might get tired of all the chaos in the Gryffindor common room or just need some time away from his friends to think. 'Taking the air' would be a good way for him to do that. Luna Lovegood could also be a character who 'takes the air'. She has a unique perspective on things, and being outside in nature might be something she enjoys, perhaps to observe some magical creatures or just to be in her own world.
Most likely, Harry Potter, Hermione Granger, and Ron Weasley will still be the main characters. After all, they are the central figures in the original series. But there could also be new characters introduced who are either part of their wealthy new circle or those who are affected by their millionaire status.