Lewis and Fred could be an interesting combination. Lewis is quite powerful in the Mystery Skulls world, and Fred is known for his trap - making skills. They could collaborate on creating some really elaborate and effective traps to catch the bad guys. Lewis could use his powers to enhance the traps, while Fred could use his mechanical know - how to build them.
Vivi and Velma would make an interesting pairing. Vivi has her own knowledge of the supernatural world, and Velma is the brains of the Scooby Doo gang. They could share their insights and research methods, and Vivi might introduce Velma to some new concepts in the supernatural realm that Velma has never considered before.
Naruto and Shaggy could be an interesting pairing. Naruto's high - energy and brave nature could contrast with Shaggy's cowardly but kind - hearted personality. They could learn from each other. Naruto could teach Shaggy to be more courageous, and Shaggy could introduce Naruto to some delicious human world food.
Naruto and Scooby would be a really interesting pairing. Naruto's energy and enthusiasm would contrast with Scooby's cowardice. Naruto could encourage Scooby to be brave and Scooby could teach Naruto about having fun even in scary situations. Also, Naruto's ability to make shadow clones could be used in really creative ways to help solve mysteries, like sending clones to different areas while Scooby and the gang follow the main clue.
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.
Fred and Erza would make an interesting pairing. Fred is used to being the leader in solving mysteries, and Erza is a strong and fearless leader in Fairy Tail. They could combine their leadership skills to lead the group in solving a complex mystery or fighting a powerful enemy.
Cas (Castiel) and Shaggy would be an interesting combination. Cas is an angel who doesn't always understand human behavior, and Shaggy is this skittish but kind - hearted character. Cas might be confused by Shaggy's fear of everything, but also find his simple kindness endearing. Shaggy, on the other hand, might be initially terrified of Cas but then realize he's a friend. It could lead to some really cute and comical interactions in the fanfiction.
I think Pikachu would be really interesting. It's so cute and energetic. In the fanfiction, it could use its electric powers to light up spooky places that Scooby Doo and the gang are exploring. Also, its reactions to all the strange things in Scooby Doo's world would be hilarious.
One interesting aspect is the character interactions. For example, when Scooby Doo and his gang cross over with characters from other shows, we get to see how their personalities clash or complement each other. It can be really funny to see the cowardly Scooby interact with a very brave character from another series.
Shaggy and Amethyst could be a great combination. Shaggy is always a bit of a scaredy - cat but also has a big heart. Amethyst is laid - back and loves to have fun. They could bond over their love for food and their easy - going attitudes, while also helping each other out during the adventures. Shaggy might be hesitant at first when facing gem - related dangers, but Amethyst could encourage him and show him that there's nothing to be too afraid of.
Shikamaru and Shaggy would be an odd but fun pair. Shikamaru is lazy but super smart, and Shaggy is always hungry and a bit of a scaredy - cat. They could bond over their love of food (Shikamaru likes his snacks too). And when it comes to getting out of tricky situations, Shikamaru's strategic mind could come in handy for both of them, while Shaggy's ability to run away fast might be something Shikamaru could learn from.