An intelligent talking animal, perhaps a fox. This fox could be a bit of a trickster but also have a good heart. It could befriend Little Miss Marker and offer her advice in a rather cryptic way, adding an element of mystery and fun to the fanfiction.
A young, adventurous boy from a neighboring town. He could be quite different from the characters Little Miss Marker is used to. He's full of energy and new ideas, and together they could get into all sorts of escapades, like exploring an old, abandoned castle.
A brilliant detective from another city could be added. This character could be initially a rival to Miss Scarlet and the Duke, but later they all team up to solve a really tough case. He could have his own unique methods of investigation.
A young stargazer from Earth could be a new character. This character could be someone who has always been fascinated by the stars and dreams of traveling to other planets. When the Little Prince lands on Earth again, they meet and the stargazer becomes his guide on Earth, showing him all the new things that have happened since his last visit. Another potential character could be a talking moonbeam. It could offer the Little Prince advice and wisdom, as well as some magical abilities to help him on his journey.
A wise old owl could be added. It could give advice to the little white horse. Also, a mischievous fox that sometimes gets the horse into trouble but also helps it out of tight spots.
A healer character could be added. This healer could be the one who discovers a hidden power within the apprentice that could change the course of their journey. Another potential character could be a mysterious traveler. This traveler has seen many different worlds and has knowledge that could either help or hinder the apprentice.
A scientist who is an expert on alien plants. He could be brought in to study the plant and try to find a way to control it.
It's a great short story. The characters are vividly portrayed. Little Miss Marker is often a memorable character with her own unique charm and personality traits.
A mysterious traveler passing through the town could be a new character. This person has seen many strange things in their travels and is not afraid of Edward. In fact, they see his potential and encourage him to leave the town and see the world.
A new character could be a therapist who has a unique approach to helping the main character. This therapist could introduce new ideas and methods of healing that the main character hasn't encountered before.
A healer from a far - off land could be an interesting addition. This character could bring in new knowledge of magic and medicine that the existing characters are unaware of. Maybe they have a special connection to nature that allows them to heal in ways not seen before in the story.
A young Martian inventor could be a great addition. This character could create unique gadgets and machines that help the protagonists in their adventures. For example, a flying device that can travel at high speeds across Mars.