First, you need to understand the characters and worlds of both HTTYD and Frozen. Then, think of an interesting plot that can bring the two together, like maybe a dragon from HTTYD somehow ends up in the Frozen world. Next, start writing the story, focusing on how the characters from both universes interact with each other.
There are often crossovers with other fantasy universes. For example, in some 'httyd crossover fanfic', the Vikings from httyd meet the characters from 'Narnia'. The contrast between the two worlds, one with dragons and the other with magical creatures like centaurs and fauns, makes for a really engaging story. It can bring new adventures and challenges for the httyd characters.
Well, for a httyd transformers crossover fanfic, start with a strong concept. Maybe something like the Autobots land on Berk and have to figure out how to deal with the dragons. Focus on the interactions between the characters. The vikings' reactions to the giant robots and the Transformers' views on the dragons would be really interesting to explore. And make sure your writing style is engaging, using vivid descriptions to bring the crossover world to life.
One idea could be to have Toothless meet Jack Frost. Maybe Jack could try to ride Toothless and they could have an adventure together exploring the skies and the wintery landscapes. It would be cool to see how their different powers interact, like Toothless' fire against Jack's ice.
One idea could be that the dragons in HTTYD are attracted to the cold of Frozen's world and they fly there. The people of Arendelle are initially scared but then they learn about the dragons from the dragon riders. Another idea is that Elsa's ice powers somehow have an effect on the dragons, like making their fire breath turn into ice breath for a short time.
One idea could be that the dragon's fire power can be used to recharge the Transformers in some way. Another is that the Autobots could learn the concept of flying from the dragons and incorporate it into their own designs. Or perhaps the Decepticons try to capture the dragons to use their power for evil purposes, and the vikings and Autobots have to work together to stop them.
Once upon a time in the land of Berk, Hiccup was flying on Toothless when a strange magic portal opened. Out of it came Merida from the land of DunBroch. Hiccup was startled but curious. Merida was amazed by the dragons. They decided to team up. Hiccup showed Merida how to ride Toothless and in return, Merida taught Hiccup some of her archery skills. Together they went on an adventure to save both their lands from a common enemy that was using dark magic.
When writing a 'httyd crossover fanfic', you need to do a lot of research on both httyd and the other universe you're crossing with. If it's a crossover with 'Harry Potter', you should know the rules of magic in that world as well as the dragon lore in httyd. Plan your story structure carefully. Start with an interesting introduction that grabs the reader's attention, like a sudden portal opening between the two worlds. Build up the relationships between the characters gradually and create some conflict and resolution. Make sure to keep the essence of the httyd characters intact while also allowing them to grow in the new crossover situation.
With Jack Frost, his character can be developed by showing his reaction to the dragons. He might be fascinated by them at first but also a bit scared. His relationship with Toothless could be a key part. Maybe Toothless doesn't trust him immediately, and Jack has to earn that trust. This would show his determination and his ability to connect with different beings.
Next, write your story. Make sure to follow any guidelines the archive might have regarding grammar, formatting, and content. For example, if they don't allow excessive violence or inappropriate language, adhere to those rules. After writing, proofread your work carefully.