Well, you might find stories that focus on the emotional bonds between the humans and the creatures, or perhaps tales of mystery and discovery in the How to Train Your Human world.
You can find all sorts of storylines. Some might focus on the characters' adventures after the events of the movies, while others might explore alternate universes or prequels.
There are all sorts of storylines. Some might focus on the adventures of the dragon eggs, while others could explore the mystery behind their origin.
You might see characters from both universes teaming up to face common enemies or going on adventures together. Maybe there'll be power-sharing and training scenes too.
You could write a story where a human becomes a pet of a dragon and has all sorts of adventures in the dragon world.
It could be a tale of the human pet getting lost in a magical land and relying on the dragon's help to find their way back home, facing many challenges along the way.
You might find various stories. Some could focus on new adventures of the characters after the original movie, while others might explore alternate timelines or relationships.
There are various fanfiction stories. Some might focus on the adventures of the characters after the events of the movie, while others could explore alternate storylines or relationships.
Some of the notable things could be unique takes on how the dragons interact with humans in a non-magical way. Maybe there's more emphasis on social issues or character development that wasn't in the original. Also, different authors might come up with their own creative settings and conflicts.
It might be a story where the characters have to deal with the dragon's frequent and smelly farts, leading to all sorts of adventures and challenges.
You might expect adventures where the characters from both worlds join forces to face a common enemy. Maybe there could be magical elements from Eragon combined with the dragon-training techniques from How to Train Your Dragon.