The characters would face the challenge of not being recognized or being seen as a threat. If they time - travel to a time when their families or tribes didn't know them yet, they could be considered outsiders. For example, Hiccup might be seen as a strange boy with his un - Viking - like ways of handling dragons. Also, they would have to deal with the different cultural norms of the past. Things like how battles are fought, how the tribe is led, and how resources are shared could all be very different, and they would need to adapt quickly to avoid getting into trouble.
One big challenge would be not being believed. People in the past might think he's crazy when he talks about future events. Also, he has to be careful not to change too much and disrupt the whole timeline. Another challenge could be that some of the villains in the past might be more powerful than he expected, and he'd have to find a way to defeat them with his current skills and limited knowledge of the past.
Some characters might be amused. For example, Hiccup, being the open - minded and curious one, could find it interesting to see how fans imagine different scenarios. He might even get some new ideas for his own adventures.
They might face the risk of changing the future in ways they don't expect. For example, if they accidentally prevent an important event from happening, it could have a huge impact on their own present. Also, they could encounter past versions of themselves or their enemies, which could lead to some really confusing and dangerous situations.
Fishlegs would likely have a very animated reaction. If he comes across some fanfiction that has really strange dragon facts, he'd be so shocked. He might start rambling on about how wrong it is according to his extensive dragon knowledge. His eyes would be wide and he'd be waving his hands around.
As a girl in fanfiction, Voldemort would face challenges like having to adapt to a different body. Her magic might be affected by the transformation too. She'd also have to deal with the fact that her Death Eaters may have different reactions to her new form. Some might be less obedient or more overprotective. Plus, she would need to re - establish her reputation as a feared figure in a world that now sees her as a female, which could be quite difficult considering the gender biases in the wizarding community.
One challenge would be dealing with students who don't respect his authority. Naruto was always a bit of a rebel himself, so he might find it hard to enforce strict rules. Another challenge could be teaching complex ninja techniques to students with different levels of ability.
Perhaps a scientific experiment gone wrong could lead to time travel. The Vikings in the HTTYD world are known for their inventiveness. Maybe Fishlegs, being the more scientifically - minded Viking, creates a device that he thinks will enhance dragon communication but instead opens a rift in time. This would send the main characters, along with their dragons, back to a time when dragons and Vikings had a more hostile relationship, forcing them to use their modern knowledge to change the course of history for the better.
Ned Stark as king in fanfiction would face challenges on multiple fronts. There is the issue of succession. He would need to plan for the future and ensure a smooth transition of power. His own code of honor might conflict with the cut - throat politics of the court. He would have to be more diplomatic than he is used to. Then there are the regional differences within the Seven Kingdoms. Each area has its own culture and needs, and he would have to find a way to satisfy them all. For example, the North has its own traditions that he would want to uphold while also integrating it better with the rest of the kingdom.
One big challenge would be finding skilled ninjas to help him. Ushiogakure might not have a large population to start with. He'd need to either train new ninjas from scratch or convince others to join him. Another issue could be dealing with any existing rivalries or feuds in the area.
One challenge could be dealing with their different families. Gumball's family is chaotic and full of surprises, while Penny might have her own family traditions. Another is their different personalities. Gumball is impulsive at times, while Penny is more reserved. They'd need to find a balance in their decision - making as a married couple.