Well, if you're doing a crossover with 'Pokémon', Ash Ketchum would be a great addition. He could help the Rugrats understand the world of Pokémon and they could go on a Pokémon - hunting adventure together. Another good character for a crossover, say with 'Digimon', would be Tai Kamiya. He could show the Rugrats how to interact with Digimon. And for a crossover with 'Ben 10', Ben Tennyson could be included. He could use his alien forms to protect the Rugrats in dangerous situations.
When considering characters for a rugrats crossover fanfiction, if you cross over with 'Star Wars', Luke Skywalker would be a cool character to have. He could teach the Rugrats about the Force and they could go on a mini - adventure in the Star Wars universe. If it's a crossover with 'Disney Princesses', Belle from 'Beauty and the Beast' would be a wonderful addition. She could share her love for books with the Rugrats. And for a crossover with 'Transformers', Optimus Prime would be an important character. He could protect the Rugrats from the Decepticons and be a heroic figure for them to look up to.
The parents should be included. Their parenting styles and reactions to the girls' different situations can add depth. Mrs. Rooney's attempts to keep the family together while dealing with Liv's Hollywood drama and Maddie's sports - related issues can be really interesting. Mr. Rooney's comical yet supportive role can also be explored further. Additionally, Willow from Liv's world could be a good character to bring in. She could befriend Maddie and introduce her to the more glamorous side of Liv's world, causing Maddie to have a new perspective on her sister.
Shadow would be a great addition. His brooding nature and powerful combat abilities would add an interesting dynamic. He could be suspicious of Infinite at first and be in conflict with Sonic about whether to trust him or not. And then there's Knuckles, who could guard some important location or object that is related to the crossover event, like a powerful chaos emerald that is causing the dimensions to cross.
Sherlock Holmes is a great choice. His deductive skills would contrast well with Kaito Kid's thieving skills. Another good one is Lupin III. They are both master thieves, and a crossover between them could be full of interesting heist scenarios. Conan Edogawa would also be interesting. Since he's always trying to catch Kaito Kid in the original series, a crossover could explore new dynamics between them.
Ryder is a must - include character. He's the leader of the Paw Patrol, so he can be the one to initiate the crossover and bring the different groups together. Also, Chase would be great as he's very brave and good at following rules, which could be useful in a crossover situation.
The Precursors are very important in the Jak and Daxter universe, and including them in a crossover fanfiction could add a whole new level of depth. They could be the key to understanding the new world they cross into, or perhaps they have a hidden agenda that Jak and Daxter have to figure out. Also, the Metal Heads could be included in a more action - packed crossover, where they pose a threat not only in their own world but also in the crossed - over world.
Definitely Naruto and Hinata as the core. But Iruka sensei could be a wonderful addition. He was Naruto's first teacher and could offer wisdom and guidance in this new, strange crossover world. Then there's Shikamaru. His intelligence and strategic thinking would be invaluable. He could come up with plans to deal with any threats that arise in the fanfiction, and his laid - back yet perceptive personality would create interesting interactions with the other characters.
Definitely Goku and Vegeta. Their fathers' presence could add an interesting dynamic. Goku could offer some light - hearted advice to Goten and Vegeta could be pushing Trunks to be stronger. Also, Bulma could be included as she often has cool gadgets that could help the boys in their adventures.
The Flash is an obvious choice. Their relationship in the original comics and shows is full of tension and drama, so it would add a lot to the fanfiction.
Lydia Martin would also be a good character to include. She's smart and powerful, and her relationship with Stiles could be further explored in the context of the crossover. Her banshee abilities might come in handy when dealing with any new threats in the crossover world.
Sasuke would be a great character to include. His complex relationship with Naruto and his own journey of redemption could add an interesting dynamic to a fanfiction involving Hinata and Neji. Maybe he could be a reluctant ally at first and then gradually come to respect their skills and values.