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.
One plot twist could be that the Triwizard Tournament itself is a ruse. It was never really about the competition but about luring Harry into a trap. The other champions are unknowingly part of the plan. When Harry discovers this, he has to convince the other champions to join him in fighting against the real enemy behind the tournament.
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 interesting plot twist could be that the de - aged Harry has some hidden memories of the future that help him in the tournament in unexpected ways. For example, he might remember a particular spell that an opponent will use and be able to counter it easily.
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.
A plot twist could be that the Triwizard Cup is actually a portal to a different dimension, and Harry and Hermione accidentally get transported there during the final task. They then have to find a way back while dealing with strange creatures and magic in this new dimension.
Maybe in the fanfiction, there's a plot twist where Hermione discovers a hidden rule in the Triwizard Tournament that allows her to form an alliance with all the champions instead of competing against them. This would change the whole dynamic of the tournament and lead to a completely different kind of story.
One possibility could be that Harry discovers some dark magic or a hidden conspiracy within the Triwizard Tournament that forces him to take extreme measures and destroy it. Maybe he finds out that the tournament is being used as a cover for an evil plot against Hogwarts or the wizarding world in general.
A plot could be that the Triwizard Tournament tasks are magically altered to target Harry specifically, and Hermione has to use her skills to figure out who is behind it. Maybe a new dark magic is involved that she has to research. She then has to train Harry in new ways to face the challenges. For example, teaching him some ancient spells that are not commonly known.
Another plot could revolve around a spell gone wrong during the Triwizard Tournament tasks. For example, the spell that creates the maze for the final task malfunctions and the maze becomes a living, sentient entity that changes and adapts to the champions' movements, making it much more difficult and dangerous to navigate.
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.