King would be a really fun character to include. His small size but big ego can create humorous situations in the human world. He could get into all sorts of mischief, like trying to convince humans that he's a powerful demon lord while also being fascinated by human things like toys and junk food.
Amity could also be a great addition. Her growth from a somewhat cold character to a more empathetic one can be further explored in the human world. She might struggle with fitting in at first but then find her place among human witches or those interested in magic.
Luz is an obvious choice. She can bring her knowledge of the Boiling Isles to the human world and show other humans the wonders of magic. Her enthusiasm and kind heart would make for great interactions with other human characters.
If it's a crossover with 'Frozen', Elsa would be a great character. Her ice powers could contrast with the warm - themed magic in 'The Owl House' in an interesting way. Anna's adventurous spirit would also fit well into the story. From 'The Legend of Korra', Korra could be included. Her ability to bend multiple elements and her strong - willed personality would make for some exciting interactions with the characters of 'The Owl House'. She could even learn new forms of magic from them.
One idea could be a human character accidentally stumbling upon a hidden portal to the Boiling Isles and having to adapt quickly to the strange new world. They could form an unlikely friendship with a witch or demon and learn magic along the way.
Obviously, Spyro himself is a must - include character. He's the main character of the Spyro universe. Elora could also be included. She has her own magic and can interact with humans in interesting ways. Then there's Hunter, who could provide some action - packed scenes when paired with a human character in the fanfiction.
The friendly neighbor who lives on the outskirts of the woods can also be a great addition. They could bring news from the outside world, or be involved in a budding romance with one of the characters from the little house.
King might also be a character in time travel fanfiction. His search for his true identity could be further explored through time travel. He could go back to the time when his species was more prevalent in the Boiling Isles to learn about his origins, which would be an exciting adventure in the context of time travel fanfiction.
Luz would be an obvious choice. Since she has a connection to both the Human Realm and the Boiling Isles, she could be in the Human Realm for some reason, like bringing a bit of the magic she's learned back home and facing new challenges there. Another option could be a new human character that gets involved with the magic of the Owl House, maybe a neighbor of Luz who notices strange things going on at her house and gets pulled into the adventure.
Kion is often a popular choice. His leadership and connection to the Roar make him an interesting character to interact with human characters. He could teach a human about the importance of protecting the circle of life.
April O'Neil is a classic choice. She's a human character who has a long - standing relationship with the turtles. Her skills as a reporter can add an interesting dynamic to the story.
One idea could be a human character from the Human Realm accidentally discovers a portal to the Boiling Isles and has to adapt to the strange new world while also trying to find a way back home. Another could be a story where a group of human friends get caught up in the magic of the Boiling Isles after a spell goes wrong in the Human Realm. Or perhaps a human with latent magical abilities is drawn to the Owl House in the Human Realm and begins to learn about their true powers.
A scientist would be a great character. They could study the unique flora and fauna of the Jak and Daxter world and try to find ways to use their knowledge to help the inhabitants. For example, they might discover a new way to harness eco energy.