Amy Rose can be included as well. Her love for Sonic can create some interesting dynamics. She might be jealous of the time Sonic spends with Shadow or she could also be a key player in a mission, using her hammer and her determined personality to help Sonic and Shadow in their adventures.
Tails is a very popular character to include. He is Sonic's best friend and his technical skills can add a lot to the story. For example, he could help Sonic and Shadow figure out some complex machinery or technology that is part of the plot.
Knuckles is also a great addition. His strength and his role as the guardian of the Master Emerald can bring in new story elements. He could be involved if the plot has something to do with protecting a powerful artifact or location. Maybe he initially doubts Sonic and Shadow's intentions but then realizes they are on the same side.
Sonic, without a doubt, is the most crucial character. But in addition to him, characters like Silver can bring a different perspective. His ability to manipulate time in a way could be incorporated into the Black Knight story in unique ways. Also, Rouge. Her thieving skills and her relationships with other characters can be a great addition. And don't forget about the characters native to the Black Knight world, like King Arthur - like figures, who can add a touch of medieval fantasy to the fanfiction.
In sonic the hedgehog crossover fanfiction, Sonic himself is of course the main character. But other characters that are popular to include are Amy Rose. Her love for Sonic can create interesting relationship dynamics in crossovers. Another popular one is Dr. Eggman. His villainous nature can be a great source of conflict in crossovers with other characters. And then there are characters from other video game series that are also quite popular, like Link from The Legend of Zelda. His use of weapons and exploration skills could make for some really exciting crossovers with Sonic.
Definitely Sonic. He's the star of the show. Then there's Amy. She can bring in the element of love and determination. Shadow could also be a great addition. His brooding and powerful nature can create some interesting storylines, especially if he has to team up with Sonic in the Lost World. And don't forget about Cream and Cheese. Their cute and innocent presence can contrast with the more dangerous aspects of the Lost World.
Sonic, of course, is a must - have. But also Knuckles from both universes. In Sonic Boom, Knuckles is a bit more of a muscle - brained character in a fun way, while the classic Knuckles is more serious about guarding the Master Emerald. When they meet, there could be some hilarious misunderstandings at first, like Sonic Boom Knuckles trying to show off his strength to the other Knuckles, but then they end up teaming up against a common threat.
Bowser can also be a great addition. He can be the antagonist who tries to cheat in the Olympics or cause trouble for Sonic and Mario. And from Sonic's side, Knuckles is a fan - favorite. His strength and gliding ability can make for some interesting interactions with the Mario characters. For example, he might get into a friendly competition with Donkey Kong over who is stronger.
Mario and Sonic themselves are the most obvious and popular choices. They are the main characters of their respective franchises and their rivalry is always exciting to explore.
Princess Peach from the Mario universe is often included. She can add a touch of elegance and sometimes be a damsel in distress or a helpful ally. Tails from Sonic's world is also popular. His intelligence and flying ability can be useful in various situations in the fanfiction, like helping Sonic and Mario solve puzzles or reach high places during the Olympic events.
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.
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.
Sonic himself is always a popular character in this type of fanfiction. Whether it's Sonic from Sonic Boom or the modern Sonic, he's the central figure. Tails also tends to be popular as he's Sonic's sidekick in both versions. His intelligence and ability to create gadgets can play important roles in the crossovers.