Well, in 'the mummy fanfiction' there could be a concept where the mummy is part of a hidden society of ancient beings. This society has rules and a hierarchy that the mummy has to abide by. It could also introduce the idea of a time - traveling aspect, where the mummy gets sent to different eras and has to adapt. Or perhaps there's a concept where the mummy's appearance changes depending on the emotions it feels. For example, when it's angry, it becomes more monstrous, and when it's calm, it looks more human - like.
One interesting concept could be a crossover of magic from 'Harry Potter' and the ancient curses in 'The Mummy'. For example, perhaps the spells from Hogwarts could be used to combat the undead forces from 'The Mummy'.
One idea could be exploring the backstory of the mummy in more detail. Maybe she had a family or a great love before she was mummified. Another could be a different take on the relationship between the mummy and the main characters, like if they formed an unexpected alliance. And perhaps a fanfiction where the mummy's powers are used for good instead of evil in the modern world.
One idea could be a crossover with 'Indiana Jones'. The mummy could be part of an ancient mystery that Indy is trying to solve. Maybe the mummy has some sort of power or knowledge that Indy wants.
There might be a fanfiction where a mummy is awakened in the Twilight universe and forms an alliance with the Cullens. It could bring a whole new dynamic to the story as the mummy shares its ancient knowledge with the vampire family.
One idea could be a crossover with the 'Indiana Jones' series. The Mummy's curse could somehow be related to an ancient artifact that Indiana Jones is after. Maybe they have to team up to stop the mummy from unleashing a greater evil.
One idea could be that the mummy monster girl is an ancient protector of a hidden tomb. A young archaeologist stumbles upon the tomb and accidentally awakens her. She initially sees him as a threat but then realizes he has a pure heart. They form an unlikely alliance to protect the tomb from those who would loot it for evil purposes.
One interesting 'Harry Potter Mummy Fanfiction' could be about a mummy that has magical powers and teams up with Harry Potter to fight dark forces. Maybe it uses its ancient Egyptian magic in the wizarding world.
One interesting storyline could be Imhotep and Evelyn teaming up to fight a new, more powerful ancient evil. Maybe they discover a prophecy that only their combined knowledge of the old and new worlds can stop it.
Well, in a 'the mummy fanfic', you might consider a plot where the mummy's curse spreads to other artifacts in a museum, causing chaos. You could also explore the idea of the mummy having a family or a past life that was not previously known. Another interesting angle could be to write about the mummy being transported to a different time period, like the future, and how it copes with the advanced technology and different social norms.
In the backrooms fanfiction, the concept of the 'safe rooms' is really cool. These are areas within the backrooms where the entities don't seem to go or where the environment is a bit more stable. It gives the characters a brief respite from the constant danger and allows for some interesting plot developments as they plan their next moves.