One idea could be a character who discovers they have a latent ability to communicate with vetalas and must use this to stop an ancient evil vetala from rising. Another could be a vetala falling in love with a human and the challenges they face in their relationship within the supernatural world.
A story could center around a young witch who tries to become a vetala for power but realizes too late the dark consequences. She then has to fight against the very nature she has embraced to save her loved ones and the world from the havoc the vetala side of her is causing.
Perhaps a plot where a group of hunters accidentally awakens a powerful vetala and they have to team up with a vetala who doesn't want chaos to find a way to put it back to sleep. This would involve a lot of action and tense moments as they navigate the vetala world's rules and powers.
A young and curious human who stumbles upon the world of vetalas could be a main character. They might start off as an innocent bystander but get drawn deeper into the vetala lore.
One idea could be Elena discovers a hidden power within herself that she has to learn to control. It could lead to her having to face new enemies or challenges in the 'vd' world.
One idea could be that the Avengers have to deal with a supernatural force that is causing chaos in the city. Maybe it's a powerful demon that they can't defeat with their usual weapons and tactics. They then seek help from the Supernatural world, like Sam and Dean Winchester, who teach them about exorcisms and using holy water.
A cross - over could involve a curse in the 'Arrow' world that has a supernatural origin. Oliver Queen and his team seek the help of Sam and Dean Winchester who are experts in dealing with the supernatural. Along the way, there are clashes in their methods of operation but they gradually learn to trust each other and combine their skills to break the curse.
One idea could be that a supernatural entity from the Supernatural world somehow ends up in Central City and starts causing chaos that only the Flash's speed can help contain. For example, a demon that can possess multiple people at once and the Flash has to use his speed to track down all the possessed bodies before the demon can complete a dark ritual.
One idea could be Naruto having to adapt to the different social expectations placed on girls in the ninja world. For example, she might struggle with the more restrictive clothing styles at first but then find ways to make it her own while still being a capable ninja. Another plot point could be how her relationships with other characters change. Sasuke might initially be confused by Naruto's new form but then come to see that she's still the same person deep down. Also, Naruto as a girl could inspire a new generation of female ninjas in the village, showing them that they can be just as strong and important as male ninjas.
A possible plot could be Sam's relationship with Dean in this new form. Dean might be initially skeptical or even a bit scared of Sam's transformation. Sam could then try to convince Dean that he's still the same person on the inside. Also, Sam could be on a mission given to him by a higher - up angel. But he starts to question the motives of the angelic hierarchy as he realizes some of their actions might not be as noble as they seem. He could then use his new powers to try and change things from the inside.
A really cool plot might be that the forces of Hell in Supernatural are trying to take over Gravity Falls because of its unique supernatural properties. Sam and Dean, along with Dipper and Mabel, would need to use their combined knowledge and skills. Sam's research abilities and Dean's combat skills, along with Dipper's knowledge of the town's secrets and Mabel's out - of - the - box thinking, to stop the demonic invasion.
One idea could be that Danny and the Winchester brothers team up to fight a ghost that is causing chaos in both the Ghost Zone and the human world. Maybe it's a powerful entity that has the ability to cross between dimensions easily.
One idea could be a crossover with 'Doctor Who'. The Doctor and the Winchesters could team up to fight a time - traveling demon. Another could be a crossover with 'Buffy the Vampire Slayer', where Buffy and the boys from Supernatural join forces against a powerful vampire coven that has some sort of connection to the supernatural underworld in both universes. And a crossover with 'The X - Files' would also be cool, with Mulder and Scully investigating a case that turns out to be related to the monsters the Winchesters usually hunt.