Well, for a Twilight and It crossover fanfiction, you could start with the setting. Suppose the town of Forks is somehow connected to Derry. The vampires in Twilight are often in search of new territories. What if they stumble upon Derry which has its own dark secrets in the form of Pennywise? The Losers Club could initially be terrified of the vampires, thinking they are some new form of evil. But then they realize that they might need to work together to defeat Pennywise who sees the vampires as new prey. It could be a story full of mystery, horror, and unexpected alliances.
A possible concept for a Twilight and It crossover fanfiction is that the Volturi, the powerful vampire coven in Twilight, become interested in the strange happenings in Derry. They send some of their members to investigate, including Jane and Alec. Meanwhile, the Losers Club is dealing with Pennywise's latest attacks. When the Volturi encounter Pennywise, they are intrigued by his power. However, they also see him as a threat to their kind. The Losers Club, on the other hand, is hesitant to trust the vampires at first. But as the situation worsens, they must find a way to combine their efforts to stop Pennywise and keep the Volturi from causing more chaos in Derry.
One idea could be that Naruto characters enter the Twilight world and are shocked by the existence of vampires and werewolves. For example, Naruto himself might be intrigued by the different powers and try to understand the complex relationships between the Cullens and the werewolf pack. He could use his ninja skills to interact with them in unique ways.
One idea could be a story where the characters from 'Descendants' end up in the 'Twilight' world. For example, Mal could meet Bella and they could form an unlikely friendship. Mal might be intrigued by Bella's relationship with Edward and the whole vampire - human dynamic in the 'Twilight' world.
A cool concept for twilight and flash crossover fanfiction could be a time - travel aspect. What if a character from The Flash travels back in time and accidentally alters the history of the Twilight world? This could lead to all sorts of chaos, like vampires ruling the world instead of just being in hiding. Or, a Twilight character could use the Flash's speed - related technology to gain an edge in their own battles, like using it to quickly escape from a werewolf pack.
One idea could be that Buffy and the Scooby Gang find themselves in Forks and have to deal with the vampire situation there. They might initially clash with the Cullens due to different ways of handling vampires. Another could be a love triangle between Buffy, Edward, and Angel. It would add a new layer of complexity to the relationships already present in both series.
One idea could be to have Alucard from Hellsing meet the vampires in Twilight. Maybe Alucard would be amused by their 'tame' nature compared to his own blood - thirsty self. He could show them what a real vampire is capable of in a fight.
Another concept could be that a powerful demon from Buffy's world is attracted to the unique vampires in Forks. This demon starts causing chaos, and Buffy and the Cullens have to team up to stop it. During this time, they learn from each other's fighting styles and supernatural knowledge. For example, the Cullens could teach Buffy more about their kind of vampire lore, while Buffy could show them some of her combat techniques against demons.
Well, perhaps there could be a plot where a character from The Flash, like Barry Allen, discovers the existence of the Twilight world. He might be intrigued by the vampires' powers and try to study them in a scientific way. Meanwhile, the vampires in Twilight might see Barry as a threat or an opportunity. For example, they could try to use his speed for their own purposes, like hunting more efficiently. This could lead to a complex relationship between the two universes.
A more complex idea could involve a threat that endangers both the NCIS world and the Twilight world. So, the NCIS team has to team up with the Cullens and the werewolves to fight against this common enemy. This would bring in all the action - packed elements from NCIS like investigations, shoot - outs, and also the supernatural elements from Twilight like vampire powers and werewolf transformations.
One idea could be to combine the supernatural elements of Twilight with the high - flying action of Sky High. For example, a vampire student could enroll in Sky High, causing chaos among the students and teachers who are used to dealing with more typical superpowers.
Another interesting concept is a character from Harry Potter, like Harry himself, ending up in Forks. He could discover the existence of vampires and werewolves there. He might try to use his magic secretly while also being fascinated by the different supernatural rules in that world. He could even form an unlikely friendship with Bella or Edward, sharing his knowledge of magic with them.