How to deal with Hiccup being cold in How to Train Your Dragon fanfiction?

First off, you might introduce a wise healer character who knows the remedy. Or, you could have Hiccup's friends embark on a dangerous quest to find the cure. Another option is to have Hiccup's inner strength and determination help him fight off the poison gradually.

Maybe Hiccup could learn some self-defense skills and stand up for himself. Or, he could find an adult he trusts to help him solve the problem. It all depends on how the story unfolds and what kind of tone you want to set.

You could have other characters try to wake him up with various methods, like using magic or seeking help from a wise elder.

You might make the illness a metaphor for a larger challenge Hiccup needs to overcome within himself. It could lead to personal growth and a deeper understanding of his role in the dragon world.

One way could be to introduce a magical cure or an event that breaks the brainwashing. Maybe a key moment from Hiccup's past triggers his return to normal. Also, the support of his dragon could play a crucial role in restoring his mind.

One way could be to have him get some much-needed rest and recovery time. Maybe he takes a nap or spends a day doing nothing but relaxing.

You could have other characters come to his rescue and help him recover.

This is a tricky one. Maybe the other characters could come to Hiccup's aid and help him break free. Or it could be a journey of self-discovery for Hiccup while in that situation.

You might have the dragons play a crucial role. They could sense Hiccup's distress and lead the others to where he is. Or, there could be a secret weapon or magic that the heroes discover to defeat Viggo and free Hiccup.

You could have other characters come to his aid quickly and offer comfort and support.