If Harry Potter kills the Joker in a fanfiction, it could be due to a misjudgment on the Joker's part. The Joker, not understanding the power of magic, might underestimate Harry. Harry, on the other hand, might view the Joker as a great threat to the innocent people in the new world he has found himself in. So, he uses his most powerful spells, perhaps the Avada Kedavra, to end the Joker's reign of terror.
Well, in a fanfiction world, anything can be possible. Maybe Harry Potter uses his magic skills like the Killing Curse. But it's really a strange crossover. The Joker is from a completely different universe with no magic, and Harry Potter is from a world full of magic. It would be a very unique and perhaps disturbing story to see how Harry Potter overcomes the Joker's chaos and madness with his magic and finally kills him.
It could be that a powerful wizard in the Harry Potter universe sends Harry to defeat Palpatine for some greater good. Harry's quick thinking and his array of spells like Expelliarmus or the Killing Curse (although he hates to use it) could potentially be used against Palpatine. Since Palpatine is used to dealing with lightsabers and the Force, Harry's magic could catch him off - guard.
In some dark fanfiction scenarios, Vernon might kill Harry Potter out of his extreme hatred and fear of magic. Maybe he discovers Harry's magic in a moment of rage and overreacts, using a weapon or his brute force to end Harry's life. However, this goes completely against the essence of the original series where Vernon was more of a bumbling, non - magical threat.
Well, it could happen in a world where magic and the chaos of Gotham collide. Maybe Harry uses his magic to get into the Joker's mind and find the good that's left in him. He could use a spell like Legilimency to understand the Joker's past traumas and then use healing magic to start the process of redemption.
Well, one possibility could be that Naruto's powerful ninjutsu skills give him an edge. He might use his Shadow Clone Jutsu to confuse the Joker and then land a fatal blow with a Rasengan. Another aspect could be Naruto's strong sense of justice which drives him to take out the chaotic Joker in the Justice League universe.
In a fanfiction scenario where Harry Potter knows the Joker, it would be a very interesting crossover. Harry, being used to a certain code of ethics in the wizarding world, might be shocked by the Joker's complete lack of moral boundaries. He could attempt to reform the Joker using magic, perhaps a spell to make him see the error of his ways. On the other hand, the Joker might see Harry as just another plaything in his game of chaos and try to break Harry's spirit.
Well, it could be a total chaos. Harry Potter's magical world is all about order in a way, with Hogwarts rules and the fight between good and evil in a more traditional sense. The Joker, on the other hand, is the agent of anarchy. Maybe he'd start causing mayhem in Hogwarts, like turning the moving staircases into death traps or making the portraits go berserk. And Harry would have to use his magic in really unorthodox ways to stop him.
One consequence could be that the Joker's followers would be out for revenge. They might target Harry Potter or his friends if they also exist in that fanfiction world. Another consequence could be that the balance of power in the Joker's world is completely disrupted. There could be a power vacuum that other villains or even some anti - heroes might try to fill.
If we look at 'harry potter kills a nundu fanfiction', it's likely that the story would revolve around Harry's motivation for such an act. Maybe the Nundu was terrorizing a village or was being used by dark wizards. Harry's act of killing it could be a turning point in his character arc, making him more confident in his abilities, yet also more aware of the weight of taking a life, whether it's a beast or not. This could lead to internal conflicts within Harry as he grapples with the morality of his actions.
Well, it could start with the Joker causing mayhem in a village in Naruto's world. Naruto, being the hero, tries to reason with the Joker at first. But when he realizes the Joker is beyond reasoning, he uses his ninjutsu skills. He might start with some basic fire - style jutsu to test the Joker's limits and then progress to more powerful attacks like his Nine - Tails Chakra Mode attacks until the Joker is defeated.
Maybe in that fanfic's plot, there was a misunderstanding that got out of hand. Suppose Harry was framed for something terrible, and Hermione, believing the false evidence, felt that she had to take drastic action to protect the wizarding world from what she thought was a great threat, so she kills him. But later she realizes her mistake.