Well, it would become a more equal relationship at first. Since Hiccup is now a dragon, he can understand Toothless on a whole new level. They might compete in dragon activities like flying races or hunting together. However, Toothless might also be a bit confused at first, not sure how to act around his once - human friend who is now a dragon.
Their relationship could become more complex. Hiccup, as a dragon, might have new instincts that conflict with Toothless's. For example, they could have different ideas about territory or leadership within the dragon group. But at the same time, their bond of friendship would still be there. Hiccup could use his human intelligence in his dragon form to come up with new ways to play and interact with Toothless, like creating new games that only dragons could play.
If Hiccup turns into a dragon, his relationship with Toothless would be transformed. They would share a kinship that was different from before. Hiccup would now fully understand the sensations and experiences that Toothless has. They could communicate without the need for body language translation as much. Toothless might become more protective of Hiccup in this new form, seeing him as a fellow dragon in a world that can be dangerous for them. And Hiccup, in turn, could use his knowledge of both worlds to help Toothless in ways he couldn't before, like understanding the motives of other humans who interact with dragons.
His relationship with Toothless would become more complex. They would now be of the same species, which could lead to either competition or a deeper bond. Maybe Toothless would initially be confused about Hiccup's transformation but then accept him as an equal. They might communicate in new ways, without the need for Hiccup's human - made gadgets.
If Hiccup had powers, their bond could become even stronger. For example, if Hiccup could share his thoughts directly with Toothless using his new power, they would be able to coordinate in battles more seamlessly. Toothless might also become more protective of Hiccup, knowing that his rider now has powers that could attract unwanted attention. They could communicate in ways that no other dragon - rider pair could, like sharing memories or feelings instantaneously.
Their relationship might become more equal in some ways. As dragons, they are both facing a new and strange existence, so they have to rely on each other more. They might develop a new understanding of each other's strengths and weaknesses.
If Hiccup is under Pitch Black's control, it would be a huge shift in his relationship with Toothless. Normally, they have a deep, trusting bond. But now, Hiccup might start to command Toothless in a harsh and uncharacteristic way. Toothless would sense that something is wrong with his rider. He would try to resist Hiccup's commands at times, which would create conflict between them. Eventually, Toothless might be the key to breaking Pitch Black's control over Hiccup as he tries to reach the real Hiccup within.
His relationship with Toothless would change drastically. Instead of being the rider, he becomes like a little sibling or a young apprentice to Toothless. Toothless would have to be more protective and patient with Hiccup.
His relationship with Toothless would be very different. Toothless might be more protective of him in his new form, as if sensing that Hiccup is more vulnerable as a female Night Fury. And Hiccup would have to communicate with Toothless in new ways, perhaps using more body language that is typical of female Night Furies.
His ability to understand dragons completely transforms their relationship. Before, it was based more on observation and trial - and - error. But now, he can have real conversations. Dragons can convey their unique perspectives on things like the best hunting grounds or how to deal with other dragon species. This mutual understanding makes them not just friends but almost like comrades, sharing a common goal.
With his human friends, it would be really tough. They might be scared of him at first. Astrid, for example, would be conflicted. She was attracted to Hiccup as a human, but now he's a dragon. She would have to overcome her fear and try to find a way to communicate with him. And Hiccup would feel isolated from his human friends, longing for the connection they once had.
It could develop gradually. At first, they might be cautious around each other. For example, Human Toothless may be a bit shy because he's not used to interacting with humans in this form. The female Hiccup might be intrigued by his connection to dragons. As they spend more time together, like when they are training young dragons, they start to trust each other more. And trust can easily lead to deeper feelings.
During the pregnancy, their relationship would shift to be more centered around the upcoming baby. Hiccup would be constantly thinking about how to keep Astrid and the baby safe, especially with his role as a leader. Astrid would be dealing with the physical and emotional changes of pregnancy, and Hiccup would be her main support. This would bring out new aspects of their love for each other, like a deeper level of understanding and patience.