The main characters are probably Sonic and an alternate version of Sonic. There could also be other Sonic characters like Tails or Knuckles making appearances to support the Sonics in their rescue mission. But Sonic and his doppelganger would be at the forefront, using their speed and skills to achieve the rescue.
There could also be some new characters introduced in this fanfiction. Maybe a mysterious figure who has the power to control Dark Sonic or someone who has a connection to the origin of Dark Sonic. These new characters can bring fresh plot twists and new relationships to the story.
Sonic himself is usually really popular. Whether it's the Sonic from Sonic X or Sonic Underground, he's the main hero and often at the center of the action. People love reading about his adventures and how he deals with the challenges in the combined universes.
Classic Sonic and Modern Sonic are the stars, of course. However, Knuckles can also be a very popular character in these fanfictions. His role as the guardian of the Master Emerald in the classic world and his continued importance in the modern Sonic universe make him an interesting addition. He can be the one who initially doubts the partnership between the two Sonics but then comes around. And Amy Rose is another character that often appears. Her feelings for Sonic, both Classic and Modern, can add a touch of romance or at least some emotional depth to the story.
Well, for me, Rouge is an interesting character to write about in Sonic X and Sonic Boom fanfiction. Her thieving ways and her double - agent - like nature add a lot of intrigue. Cream and Cheese are also cute characters that can bring a touch of innocence to the stories. You can write about how they interact with the more serious characters. And don't forget Metal Sonic. You can explore his relationship with Sonic, whether it's a rivalry or something more complex.
There might also be new characters created specifically for the fanfic. These could be hybrids of the two universes or characters that are designed to bridge the gap between Shrek's world and Sonic's world. They could play important roles in the plot, like being the ones who bring Shrek and Sonic together in the first place or being the key to solving the problems that arise during their adventure.
Sonic himself is always popular. His speed and heroic nature are central to many fanfics. Then there's Sally. She is often a key character, especially in stories that involve strategy and leadership. Bunnie is also well - liked. Her mechanical enhancements can add an interesting element to the story. And of course, Antoine, with his comical French accent and sometimes clumsy but brave nature, makes for great character interactions in the fanfic world.
Amy is another character that shows up a lot. Writers might explore her relationship with Sonic more deeply, like how she supports him during the rebuilding process or if she has any new dreams or goals in the post - adventure world.
In a Metal Sonic x Sonic Fanfic, the action and adventure aspects can be really exciting. Writers may create new challenges for Sonic and Metal Sonic to face together or against each other. For example, they could be forced to team up to defeat a greater evil that threatens their world. This kind of fanfic also gives a chance to delve into the emotions of the characters. Metal Sonic, although a machine, might show signs of evolving emotions or at least a form of artificial intelligence - based loyalty or rivalry towards Sonic.
A 'sonic x sonic unleashed fanfic' could be really interesting. It might explore new adventures for Sonic in the context of the Sonic Unleashed world. Maybe it shows Sonic facing new challenges or forming new relationships within that setting.