Knuckles could also make an appearance in Sonic the Merhog fanfics. He might be guarding some underwater treasure or ancient relic. Sonic has to convince Knuckles that they need to work together to protect it from a common enemy, like a group of pirates who are trying to steal the underwater treasure.
One interesting Sonic the Merhog fanfic could be about his underwater adventures. He might discover a hidden underwater city full of unique sea creatures. Another could be his journey to find a magic pearl that has the power to save the ocean from pollution.
Another theme is transformation. The idea of Sonic becoming a merhog is central, and many fanfictions explore how this transformation affects his relationships with his friends. Some stories show his friends being initially shocked but then coming to accept and support his new form.
Well, 'Merhog Sonic: The New World' is quite good too. In this fanfiction, Sonic as a merhog discovers a whole new world that is separate from his normal one. He has to face new challenges and make new friends. It's a really engaging read as it shows Sonic in a different light, adapting to a completely new environment.
Fiona Lemon is another main character. She might have her own unique set of skills or traits that complement Sonic's. She could be intelligent, brave, or have some special power that helps in their adventures together.
Well, obviously the main characters would be the Powerpuff Girls - Blossom, Bubbles, and Buttercup. And Sonic the Hedgehog would also be a central character. There could also be other characters from both universes like Professor Utonium from the Powerpuff Girls side and Tails or Knuckles from Sonic's side depending on the direction of the fanfic.
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.
Obviously, Sonic and Amy are the main characters. Sonic, the speedy blue hedgehog, and Amy, the determined pink hedgehog. There might be other characters as well, but they are likely to be in supporting roles compared to Sonic and Amy.
Knuckles might also be part of the story. As the guardian of the Master Emerald, he has a sense of responsibility. He could either be involved in the events that led to Sonic's fall or be part of the rescue mission. His strength and knowledge of the area (if Sonic falls in a location related to the Master Emerald) could play an important role.
Monika is often depicted as intelligent and manipulative in her original game context. In the fanfic, she might use her intelligence to analyze Sonic's world and help him solve problems. Sonic, on the other hand, is known for his speed, courage and his sense of justice. He would bring his adventurous spirit to their interactions.
Well, Sonic is the central figure. But other characters like Amy Rose could be important. She might be heartbroken to see Sonic turn dark and try to use her love for him to bring him back. There could also be some new characters created specifically for this fanfiction. For example, a mysterious character who has the power to either make Sonic darker or has the key to bringing him back to normal.