Maybe the mountain has some sort of dark magic associated with it that is spreading across the land. Harry Potter, having a strong sense of justice, decides to kill it to stop the spread of this dark magic. It could be like a cursed place that is corrupting the surrounding areas and he has no other choice.
One possible motive could be that the 'mountain' in the fanfiction represents a great evil or obstacle that is threatening the wizarding world. Harry, being the hero, feels it's his duty to eliminate it. For example, if the mountain is a lair for dark creatures that are attacking Hogwarts students.
One possible motive could be that Harry is under the influence of a dark spell or curse that makes him lose control of his actions. In some fanfiction scenarios, dark magic can overpower a character's true nature.
One possible motive could be a misunderstanding. Maybe Snape is framed for something really bad, like a dark magic plot against Hogwarts. Harry, in his haste to protect the school and his friends, believes Snape is guilty and takes drastic action. Another reason could be if Snape accidentally endangers someone Harry loves dearly, like Ginny or Ron, and Harry's emotions get the better of him in the heat of the moment.
In a 'Harry Potter kills Lucius Malfoy' fanfiction, the motives could be complex. It could start with Lucius's long - standing enmity towards Harry and his family. Harry may have reached a breaking point after all the years of Lucius's attempts to undermine him. Additionally, in the context of the wizarding war, if Lucius is seen as a key figure in Voldemort's regime, Harry might view his death as a strategic move to weaken the Dark Lord's forces. It could also be a way for Harry to assert his own power and dominance over the Malfoy family, who have always looked down on him.
Maybe Fudge was starting to turn against the wizarding community in more extreme ways. For example, if he was planning to persecute Muggle - borns more harshly or side with the Death Eaters secretly. Harry, being a defender of justice and equality in the wizarding world, would not tolerate such actions and might have been pushed to kill Fudge to stop his evil plans.
In the fanfic, perhaps Harry had reached his limit with Umbridge's blatant disregard for the rights and well - being of the students and magical creatures. She was a symbol of the corrupt Ministry at that time. Harry, having a strong sense of justice, could no longer tolerate her presence and actions, especially after seeing how she treated his friends and those he cared about at Hogwarts.
Well, one possible motive could be that the assassin is working for Voldemort. Moody was a powerful Auror and a threat to Voldemort's plans. By eliminating him, it would clear the way for the Dark Lord's operations. Another motive might be personal revenge. Maybe Moody had put someone close to the assassin in Azkaban in the past, and this was a way to get back at him.
One possible motive could be extreme revenge. After years of being mistreated, locked in a cupboard, and generally being made to feel unwanted, Harry might snap in fanfiction. Another could be a sense of self - preservation if the Dursleys were somehow involved in a plot against Harry's life in the fan - created plot.
One possible motive could be a severe misunderstanding. Maybe Harry is tricked into believing that Snape and Moody are involved in some dark plot against him or his friends. For example, if there were false evidence planted that made it seem like they were working for Voldemort again. Another reason could be that he was under the influence of a powerful dark magic that clouded his judgment and made him act out of character.
One possible motive could be misinformation. If Harry is fed false information about Sirius being a traitor or a danger, he might act on it. For instance, if a well - disguised Death Eater manages to convince Harry that Sirius has joined Voldemort, Harry, in his haste to protect others, could attack Sirius.
In such a fanfiction, it could be that Harry Potter has been corrupted by a powerful and malevolent force. This force might have warped his sense of right and wrong. It could also be that the author wants to explore the extreme consequences of power and how it can turn a hero into a villain. For example, if Harry Potter was constantly taunted and mistreated by the wizarding community despite all he has done, he might reach a breaking point and lash out at everyone.