Perhaps Hiccup turns into a dragon in a different dimension where dragons rule and humans are the mythical creatures. He has to adapt quickly to this new world order. He might use his knowledge of both human and dragon ways to bridge the gap between the two species in this strange dimension. He could also start a revolution among the dragons to change their view of humans when he discovers that they are being hunted in the human world.
One idea could be that Hiccup, after turning into a dragon, has to learn to communicate with his old dragon friends in a new way. Since he now experiences the world as a dragon, he might discover new dragon abilities and secrets that were hidden from him before. Maybe he has to find a way to turn back, but in the process, he helps the dragon world solve a big problem, like dealing with a new and dangerous enemy.
A plot could involve Hiccup's transformation being a result of some ancient magic gone wrong. As a dragon, he struggles to fit in with the dragon tribes. He has to prove himself worthy to the alpha dragon while also trying to reconnect with his human friends. His dragon form might have unique markings or powers that attract both the attention of those who want to use him and those who want to protect him.
One idea could be that Hiccup turns into a dragon during a battle and uses his new form to surprise the enemy. He could fly faster and breathe a more powerful fire than any other dragon, leading his team to victory.
In a fanfiction, Hiccup could be faced with a situation where the other gods are jealous of his status as the God of Dragons. They conspire to strip him of his powers. Hiccup then has to rely on his friends, both human and dragon, to regain his powers. He might go on a quest to find ancient artifacts that were used to first bestow the God of Dragons title upon him. This would involve a lot of adventure, battles, and self - discovery.
One idea could be that Hiccup discovers a new type of dragon with unique abilities. For example, a dragon that can change its color to blend in with its surroundings. This could lead to a whole new adventure as he tries to understand this dragon and protect it from those who might want to use it for bad purposes.
One idea could be that Hiccup discovers a new language that only the rarest of dragons understand, allowing him to communicate with a long - lost and extremely powerful dragon species. This could lead to him having to make difficult decisions about whether to share this knowledge with Berk or keep it a secret to protect the new dragons.
One plot idea could be that Hiccup, as a female, has unique ways of bonding with the dragons. For example, she might use her more empathetic nature to understand their needs better than in the original story. Another could be that she faces different challenges in the Viking society which is often male - dominated. Maybe she has to prove herself even more to be accepted as a dragon rider.
One interesting plot idea could be that the dragons start to communicate with Hiccup in a more complex way through their listening skills. For example, they might be able to understand his unspoken fears and desires, and then help him in ways he never expected, like leading him to a hidden treasure that only they knew about because of their unique perception.
A possible plot is that there is a magical event that switches the minds of Stoick and Baby Hiccup. So Stoick has to figure out how to take care of himself as a baby while Hiccup, in Stoick's body, has to deal with the responsibilities of being the chief. It would be full of comical and heartwarming moments as they both learn about each other in a very different way.
Well, a plot could revolve around them starting a family. Hiccup and Heather could face difficulties in having children, like dealing with some sort of magical or environmental factor that is affecting their ability to conceive. Or perhaps they adopt a child from a troubled tribe and have to help the child adjust to their new life with them.
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.
One idea could be that Hiccup discovers a new type of half - dragon that has unique abilities, like the power to control time briefly. This could lead to adventures where he has to use this new discovery to save Berk from an ancient threat that is about to be unleashed. Another plot could involve the half - dragon being a hybrid of a very rare and powerful dragon species, and Hiccup has to protect it from dragon hunters who want to use its power for evil.