One possible plot could be that Gracie is a new vampire in the Twilight world and Ryan is a human who somehow gets involved with her. They start to develop feelings for each other despite the danger of their different natures, much like Bella and Edward's story but with their own twists.
Well, another option could be to check out some Twilight - related forums. Sometimes, fans share their own fanfictions or know where to find ones specifically about characters like Gracie and Ryan. You might need to do a bit of searching within the forum, but it could be rewarding. For example, Twilight Lexicon forums might be a good place to start.
The plot could revolve around Ryan's journey to find his family. He might be a homeless kid because he got separated from his family at a young age. As an oc (original character), he has unique traits and a strong will. He meets various people during his search, some of whom try to help him while others try to take advantage of his vulnerability. Through a series of adventures and misadventures, he gets closer to the truth about his family's whereabouts.
One possible plot could be that Inuyasha somehow gets transported to the Twilight world. He might initially be confused by the modern settings and the presence of vampires and werewolves. Bella could mistake him for a new type of supernatural being. And Inuyasha, with his sword and combat skills, could get involved in the ongoing feud between the Cullens and the werewolves in Forks.
The plot might involve Twilight's friends having mixed reactions. Some could be very accepting and supportive, while others might be confused or even a bit hesitant at first. And Twilight could go on an adventure to find a way to reverse the change, if she doesn't come to terms with it right away. Along the way, she discovers new things about herself and the pony world from a different perspective.
Perhaps the mummy has a power that can affect vampires in some way, like weakening their abilities. In this Twilight and the Mummy crossover fanfiction, the Cullens could team up with some mummy - hunters to find a way to neutralize this threat. They might have to travel to ancient tombs and decipher hieroglyphics to find a solution, all while dealing with other vampires or supernatural beings who want to use the mummy's power for themselves.
Perhaps the plot involves a human character who unknowingly falls in love with a vampire or werewolf in disguise. The stranger aspect could be that this supernatural being is hiding their true nature, and as the story progresses, the human discovers the truth and has to deal with the implications of loving someone from a different world. For example, they might have to face the danger that comes with being involved with a vampire or werewolf, and also the secrecy that surrounds their kind.
It could be about Princess Twilight disappearing mysteriously. Maybe she has been kidnapped by an unknown enemy. Her friends then set out on a quest to find her, facing various challenges along the way.
It could be about a young vampire who has an unusual hobby of catching spiders. In the Twilight world, vampires have unique abilities, so perhaps this vampire uses their speed and agility to catch spiders in a way that no human could. Maybe they study the spiders, trying to find out if there's something special about them in relation to the vampire lore in the Twilight universe.
It could be about how the movement of the Earth affects the characters in the Twilight universe. Maybe the changing of seasons due to Earth's movement impacts the vampires' activities. For example, in winter, they might have less trouble hiding their cold skin as the cold weather is more common.
It could be about a character in the Twilight universe who has a special memory related to the events in the series that they are trying to hold on to or rediscover. For example, maybe a human character who had a brief encounter with a vampire and is now trying to remember all the details because it changed their life in some way.