One idea could be to create a fanfiction where the gang gets trapped in the Chest of Demons with the 13 ghosts and have to find a new way to escape. Another could be a story about how one of the ghosts was wrongly accused and the gang has to help prove its innocence. Or perhaps a fanfic where the gang discovers a hidden 14th ghost that is the key to controlling all the others.
Well, a really cool fanfiction idea could be to set it in modern times and have the '13 ghosts of scooby doo' be part of a virtual reality game that the gang has to play to stop an evil tech genius from releasing the ghosts into the real world. Also, you could write a story where one of the gang members is related to one of the ghosts and has to deal with that family secret while also trying to stop the ghosts' mischief. And then there's the idea of a time - travel fanfic where the gang goes back in time to when the 13 ghosts were first imprisoned and accidentally causes chaos that changes the course of the story in the present.
A really cool concept would be a fusion of the two worlds. For example, the villains from the Naruto world could be using Scooby Doo - like disguises to deceive people in the Hidden Leaf. It could be Orochimaru in a mummy costume or something. Naruto and his friends would have to use their ninja skills and also learn from the Mystery Inc. how to unmask the villains by looking for clues.
One idea could be that the Kiss band members team up with Scooby and the gang to solve a mystery at a spooky concert venue. The strange happenings could be related to a cursed instrument that causes supernatural events.
One idea could be that Naruto and the gang from Scooby Doo team up to solve a mystery in a ninja - haunted village. Naruto uses his ninja skills like shadow clones to search the area while Scooby and the gang use their detective skills to look for clues.
One idea could be that Naruto and his friends get transported to the Scooby Doo universe. They team up with the Mystery Inc. gang to solve a mystery that involves ninjutsu and some spooky ghosts. Maybe the villains are using ninjutsu to create illusions and scare people away from a certain place.
A Scooby Doo and Harry Potter crossover fanfic would be cool. The gang could go to Hogwarts for a school trip and end up having to solve a mystery involving a poltergeist that's scaring students. They'd have to use both their detective skills and some magic knowledge they pick up along the way. Shaggy and Scooby would probably be really excited about all the food in the Great Hall.
A cool concept could be a possession story. A powerful supernatural entity tries to possess members of both groups. Scooby Doo and the Mystery Skulls have to find a way to stop it before it's too late. This would bring out different reactions from the characters. Scooby and Shaggy might be more panicked, while the Mystery Skulls, with their prior experience, would be more strategic in their approach.
Well, perhaps there could be a crossover where Scooby and Shaggy accidentally eat some magic cupcakes in Equestria that give them the ability to talk to the ponies in a special way. Then they discover that there is a mystery surrounding a disappearing magical element in Equestria. The rest of the Mystery Inc. gang shows up to help, and they all join forces with the ponies like Rainbow Dash and Fluttershy to find out what's going on and save the day.
One idea could be that the gang discovers a mystery related to an ancient curse in their hometown. Maybe there are strange happenings around an old, abandoned mansion that was once the site of a dark ritual. Another could be a mystery involving a new, mysterious character who seems to know more about the gang's past adventures than they do themselves.
One idea could be that the Winchester brothers are hunting a ghost in a town where the Mystery Machine gang also happens to be. The Scooby gang initially mistakes the Winchesters for bad guys but then realizes they're all after the same spooky entity. They could team up, with Sam using his research skills and Dean showing the Scooby gang how to handle real weapons (in a non - dangerous way, of course).
Well, you could write a Scooby Doo fan fiction where the gang time - travels. Maybe they end up in the Old West and have to solve a mystery involving a ghostly cowboy. Or perhaps they go to the future and deal with a high - tech haunted house. You could also do a story where Scooby discovers he has some special powers that help them solve the mystery.