Kakashi and Fred would be a great pairing too. Kakashi is a skilled ninja and a great leader. Fred is the leader of the Mystery Inc. group. They could share leadership ideas. Kakashi could show Fred some ninja - style combat moves that could be useful when they're faced with villains. And Fred could teach Kakashi about using simple tools and traps to catch the bad guys, which Kakashi could then adapt to his ninja - tool usage.
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.
Sasuke and Velma could be an interesting match. Sasuke is all about intelligence and power, and Velma is the brains of the Mystery Inc. They could work together to analyze clues. Sasuke's Sharingan could help in seeing things that others might miss, and Velma could use her knowledge of mystery - solving techniques to figure out the overall plan. They might start off a bit cold towards each other but then grow to respect one another's skills.
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.
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.
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.
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.
Naruto and Shaggy would be really interesting. Naruto is all about courage and facing challenges head - on, while Shaggy is often timid and scared. Their interaction could be really funny and also lead to some character growth for Shaggy as he might learn to be braver from Naruto. Also, Sasuke and Velma could have an interesting dynamic. Sasuke's brooding and intelligent nature could pair well with Velma's analytical skills as they try to solve the mysteries together.
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.
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.
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.
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.
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.