The main character is Hilda herself. She is a brave and curious girl who is always exploring the magical world around her. Then there's Twig, her loyal deer - fox friend who accompanies her on her adventures. Another important character is Johanna, Hilda's mother.
If the 'hilda doll graphic novel' is about the doll's adventures, then Hilda herself is likely a main character. There might also be other characters like the people who own or interact with the doll. For example, a little girl who takes care of the Hilda doll could be another main character. There could also be some sort of magical or talking animal friends that the doll has in the story.
Obviously, Hilda is one of the main characters. Since she is the one being hypnotized, the story likely revolves around her experiences and how she copes with the situation.
The main character is Hilda. She is likely the central figure who drives the story forward. And the troll is another main character. It's their interactions and the relationship between Hilda and the troll that might form the core of the story in the graphic novel.
Mabel and Hilda would be fast friends. They both have a love for the strange and wonderful. Mabel would be excited to show Hilda her sweaters and all the cool stuff in the Mystery Shack. Hilda would share her adventures in Trollberg with Mabel. They might even come up with some new and crazy ideas for adventures together, like having a slumber party in a haunted forest. Wendy would probably be a bit more aloof at first, but as she gets to know Hilda, she'd start to warm up and they could go on some more adventurous outings, like climbing a really tall mountain in Hilda's world.
I don't know the author of the 'hilda novel' as there isn't enough information given. There could be many novels with 'hilda' in the title written by different authors.
The 'hilda novel' could cover a wide range of topics. It might be a coming - of - age story where Hilda learns important life lessons. It could also be a fantasy novel where Hilda has some special powers or abilities. Another possibility is that it's a historical novel with Hilda as a character living through significant historical events. However, without reading the actual novel, we can only speculate on what it's about.