How to incorporate Nidhogg into How to Train Your Dragon fanfiction?

You could have the characters wear masks for a disguise during a secret mission or adventure.

It's not too complicated. You can start by imagining yourself as a character in the How to Train Your Dragon world and describe your interactions and experiences with the existing characters.

Well, think about making Zephyr baby a key element in a new adventure or quest. Maybe it has a hidden power that only reveals itself when needed. Or, you could have the other characters form a special bond with it that changes their perspectives and actions.

You could start by imagining your character having special powers or abilities similar to those of a Dragonborn. Maybe they have a unique connection to dragons that sets them apart.

Well, you could start by imagining unique training methods and courses at the academy. Maybe have different types of dragons and their specific needs for training.

Think about creating a situation where Hiccup's bond with Stormfly is tested, and Dick provides unexpected support. Or maybe have them on a quest to find a magical item that only their combined efforts can obtain.

You could start by imagining a wild encounter between Hiccup and the feral dragon. Maybe it's an unexpected meeting in a remote part of the island.

You could start by imagining unique spells or magical abilities for the dragons. Maybe they can breathe fire with special effects or have the power to heal.

You could introduce the new constellations as elements of magic or power that the dragons or characters can draw from.

You could have Hiccup get the tattoo as a symbol of his bond with Night Fury during a significant moment in the story. Maybe after a big adventure or a life-changing event.