It could be a rogue Death Eater who infiltrated the Triwizard Tournament. This Death Eater might have seen Harry as a major threat to the return of Voldemort and decided to take matters into their own hands by faking his death. They could be using dark magic to cover their tracks and manipulate the events of the tournament.
One possible plot twist could be that Harry is actually in a magically induced coma rather than dead. Maybe a powerful dark spell was cast on him that made everyone believe he was dead, but a hidden ally discovers the truth and tries to revive him. Another twist could be that Harry faked his own death as part of a master plan to expose a great evil within the Triwizard Tournament. He could be secretly working behind the scenes to gather evidence and take down the real villains.
It could be one of the headmasters or organizers of the Triwizard Tournament who has a hidden agenda. They might be using the tournament for their own gain, perhaps to gain power or wealth, and Harry's actions to destroy it are thwarting their plans.
It could also be due to personal reasons related to his growth and self - discovery. The events of the Triwizard Tournament might make him realize that he needs to find his own path outside of Hogwarts for a while. He might feel that the school can't offer him the answers or the experiences he needs at that moment to become stronger and more independent.
There might be a fanfic where during the Triwizard Tournament, Harry gets cursed and Hermione has to find a way to break the curse. She races against time, using every spell and potion she knows. Meanwhile, she also has to deal with the tournament tasks on Harry's behalf. In the end, through her determination and love for Harry, she manages to break the curse and they both complete the tournament in an unexpected way.
Another possible antagonist could be a jealous student. Maybe someone who was not chosen for the Triwizard Tournament and feels left out. They might try to sabotage Harry and Susan's chances in the tournament out of envy.
A wizard from a far - off land, like a wizard from a hidden tribe in the Amazon rainforest. He or she could bring a completely different style of magic that the Hogwarts students and other champions have never seen. Their magic could be more nature - based, using the power of the rainforest plants and animals. This would make their approach to the Triwizard tasks very different and exciting.
One such fanfic could be 'The Aftermath of Harry's Faked Death'. In this fic, the wizarding world is in chaos after believing Harry is dead. It shows how his friends deal with the grief and how they start to uncover the truth that Harry might still be alive. It's a great read for those who like a bit of mystery and drama in their fanfics.
She could research about the dragons' species and their habits. By knowing what scares them or what attracts them, she can give Harry useful tips. For example, if she finds out that a certain type of music calms a particular dragon, Harry can use that during the task.
A young wizard from a nomadic wizarding tribe. This character could have skills in magic related to the elements in a very unique way. For instance, they can control the wind to fly without a broomstick, which would be amazing in the Triwizard Tournament tasks. They would also bring in a different cultural aspect to the story with their tribal traditions and beliefs.
In a fanfic like this, there could be a lot of drama. For example, Pansy might be conflicted because of her Slytherin loyalty and her growing feelings for Harry. Harry, on the other hand, could be dealing with his own feelings while also trying to survive the dangerous tasks of the Triwizard Tournament. Their relationship could start with a lot of bickering and then slowly turn into something more romantic as they face the challenges together.