There could be a young girl from a far - off land who has a special bond with a rare type of dragon. She and Hiccup could join forces. She might have unique skills like being able to communicate with dragons without words. And also, an old hermit who has been living alone with his dragon for years. He has a lot of wisdom about the ancient ways of dragon riding and could help Hiccup on his travels.
Astrid is an obvious choice. She already has a close relationship with Hiccup in the original story. Then there could be Ruffnut and Tuffnut's sister, who might see Hiccup in a new light and be attracted to his growing confidence. Also, some new characters from unexplored Viking tribes could be part of it. Maybe a healer from a far - off land who is intrigued by Hiccup's connection with dragons.
Naruto would be a likely ally. Naruto is always open to making new friends and with his strong sense of justice, he would see Thor as someone who can help protect Konoha. Another potential ally could be Kakashi. Kakashi is a very experienced and intelligent ninja. He would be able to quickly assess Thor's abilities and find ways to work together effectively.
A young dragon rider from a distant island who has a very different style of riding and communicating with dragons. This character could bring new techniques and ideas to Hiccup and his friends.
He could make allies with versions of his own friends from different universes. For instance, a super intelligent Shikamaru from a high - tech universe. Also, Naruto might team up with powerful warriors from universes where the concept of chakra doesn't exist but they have their own forms of energy. Another potential ally could be a female version of himself who has different skills and a unique perspective.
He could make allies with versions of his classmates from different universes. For example, a more confident and powerful version of Uraraka in a universe where she has had different training experiences. They could team up and use their combined skills to face challenges.
One idea could be Hiccup discovers a hidden tribe in a remote jungle. Another could be that he encounters a mythical creature in an uncharted ocean region. Maybe he also teams up with a group of international dragon riders to save a world - spanning dragon sanctuary.
He could meet alternate versions of his friends. For instance, an alternate Sasuke who has never left the village and is a strong ally from the start. This Sasuke could be more open and friendly, and together they could face the challenges of the new universe.
He could make allies with the local magic users if the universe he travels to has a magic system. They might be intrigued by his ninja abilities and see the potential in working together.
Hiccup and Rayla might also interact. Rayla is a skilled warrior. Hiccup, with his unique dragon - riding skills, could show her some new combat maneuvers from the air. In return, Rayla could teach Hiccup some of her elven fighting techniques on the ground.
Obviously, Hiccup and Toothless are the main ones. Astrid could also be in it, maybe she tries to figure out what happened to Hiccup and how to turn him back. There could also be other Vikings who are either scared or intrigued by the baby Night Fury that used to be Hiccup.