A different plot might be that there is a prophecy about an Elder Dragon and a wizard (Harry). The two are meant to work together to bring peace to the wizarding and dragon worlds. But first, they have to overcome their differences and the distrust that the wizarding world has for dragons. Harry has to learn about the dragon's culture and powers to be able to fulfill the prophecy.
One idea could be a dragon being used in the Triwizard Tournament instead of a traditional task. For example, instead of facing a Hungarian Horntail like in the original, the champions have to work together to soothe a wild and rare dragon that has escaped from a secret preserve.
Another plot could revolve around a character who discovers a long - forgotten spell that can only be cast with the Elder Wand, leading to a series of adventures to master the spell and its implications. For example, this spell could have the power to restore lost magic in the wizarding world.
One idea could be that a dragon escapes from Gringotts and Harry has to use his skills to track it down. Maybe the dragon has a special connection to a powerful dark magic item that Voldemort was after.
Imagine Harry travels back to the time of the Triwizard Tournament. With the Elder Wand, he could expose Barty Crouch Jr. much earlier. This would prevent Cedric's death and change the outcome of the tournament. It would also lead to a different dynamic in the wizarding world as Voldemort's plan to return would be thwarted much sooner.
One idea could be exploring the origin of the Elder Wand in more detail. Maybe a story about the first wizard who crafted it and the magic used. Another could be a fanfic where Harry decides not to keep the Elder Wand but instead tries to find a way to destroy it permanently, facing many challenges along the way. And perhaps a plot where the Elder Wand has a mind of its own and tries to manipulate Harry into using it for dark purposes.
One idea could be a crossover where Harry Potter characters enter the world of Dungeons and Dragons. For example, Harry, Ron and Hermione could find themselves in a D&D campaign, having to adapt to the different rules of magic and combat. Another idea is to create a new Hogwarts house based on the classes in D&D, like a house for the Paladins where students focus on honor and protecting others. Or perhaps a story where Voldemort tries to use D&D magic to gain more power, but it backfires on him.
One idea could be to have Harry Potter characters attend the College of Winterhold in Skyrim. Imagine Hermione being fascinated by the arcane knowledge there and trying to learn new spells. Another idea is to introduce the concept of Hogwarts Houses to the Elder Scrolls world, like sorting the Nords or Dunmer into Gryffindor, Slytherin etc. Also, the Patronus charm could be a very unique ability in the Elder Scrolls setting, perhaps used to fight off Daedric entities.
One interesting plot idea could be a story where the Elder Wand has a hidden connection to the Goblet of Fire. Maybe the wand was used in the creation of the Goblet, and this connection is only discovered when a dark wizard tries to manipulate the Goblet's magic using the Elder Wand. The protagonist then has to figure out how to break this connection to stop the dark wizard's evil plan.
In a fanfiction, Elder Dragons could be brought to Hogwarts for a special event, like an exchange of magical cultures. The students would be both excited and terrified. The dragons, being proud creatures, would probably act aloof at first. But as they get to know the students better, they might start to form bonds. For instance, a dragon might take a liking to a particular student who shows respect for its power and wisdom. This could lead to a unique friendship where the dragon teaches the student about dragon - related magic and the student shares Hogwarts' secrets with the dragon.
A great plot for a Potter Manor fanfiction could involve a mystery that surrounds the manor. For instance, strange noises at night lead Harry to uncover a long - forgotten chamber. It could also be about Harry restoring the manor to its former glory, perhaps with the help of Hermione's research on ancient magic used in the construction of such manors.