Don't read this 'book'

Plan

Elsa was spying on Hiccup and finds out about Toothless, stays at Raven Point for a bit and realizes she has the ability to turn into a Night Fury. Then she has a relationship with Hiccup, and asks him to be her boyfriend and he says yes because he thought it just meant friends.  Then Elsa has a dream about the Battle of the Red Death and realizes she must save Hiccup otherwise he and Toothless will die. Elsa also finds that if she makes a growling sound then she can control the dragon and turn it on and off at her own will. Then saves Hiccup at Battle of The Red Death, but then Hiccup kisses Astrid ferociously. 

When at Burke, Astrid steals Elsa's necklace and comb, the necklace being her mothers and the comb her cousins, Rapunzel. Then Astrid and Hiccup are partners and Astrid does all sorts of evil things to Elsa and Elsa retaliates back on Astrid, so Hiccup doesn't even want to be her friend and hates her! Then she realizes she should just stop the dragon inside her, so she has to make her heart ice by achieving her deepest goal. She strives to do her deepest goal, which is to have Anna and Hiccup love her back the way she wants them to. She tries to get Hiccup to like her again, but doesn't work. She gets offered a trip to Arendelle, but she things its futile because they will never love her back. So the only way she can achieve her goal is to not love Anna and Hiccup, so thinks of all the bad things they've done to her (and pains her deeply) until her hearts frozen.

Elsa then gets kicked out of Burke, as Astrid told Hiccup that because Elsa affended him he could kick her out. So Elsa becomes her own Snow Queen in her own Ice Castle, meeting Jack Frost and 'loving' him as the Frost King. 

But Elsa wishes for a happy dream, and she gets a dream of Anna, Astrid and Hiccup talking and Anna's trying to persuade Hiccup who really murdered a series of Vikings, which was Astrid. But Hiccup thinks its Elsa still and doesn't get persuaded by Anna in the dream. Elsa is happy for 2 seconds. 

Elsa is saddened by the 'happy dream' and her ice heart starts to thaw. Jack Frost realizes this and attacks her, saying she is 'too weak and doesn't serve ice well enough' and leaves her with serious injuries. Hiccup and Astrid and the whole of Burke know about Elsa's ice palace, and are trying to kill her because of a series of murders of Vikings and thinks its her.  Astrid, Hiccup, Toothless and Stormfly find the Palace and Elsa and the Burkians have an epic battle, showing Elsa's ice powers and sending Stormfly into a deep coma. Elsa is outnumbered, and then she tells them her life. They all don't believe her, and she tells them to kill her to see that she has a melting ice heart. Astrid of course does it, and Elsa does have an ice heart. Astrid tries to hide this from Hiccup, but Toothless knocks Astrid out and Hiccup sees Elsa and kisses her goodbye from the world. (epic love moment, saying that now he loves Astrid and could have maybe been friends if there was another life) But then Elsa is healed, and she says it because of 'true love.' But Elsa still heard what Hiccup said, and tells him that. Anna meanwhile had heard about an ice castle and just came there too, helping in the true love to revive Elsa from death. Elsa says it would have been her coronation day as  joke, but then that she only wishes for Anna and Hiccup to have a happy life, and she could tell the only way Hiccup could get a happy life is that he could spend his life with Astrid, and Anna could have a great life by being the Queen so she turns into a Nightfury for the first time with other people being aware of that, and then separates from her body (the Nightfury), and dies, leaving only a Night Fury which flies away. 

AFTER STORY:

3 years later.

Hiccup personally kills Astrid, and Anna lives at Burke and gives up Arendelle to remember Elsa. They want a way to make the last female Night Fury, Elsa, to turn back to the human Elsa. Then Anna makes a conspiracy that Elsa managed to not being able to become a Night Fury by her deepest goal, but also basically killed herself the same way. To what she thought was peace. So then they realized that the only way to get her back was through her own peace, and she said she could get that by Anna happily ruling Arendelle and Hiccup enjoying his life with Astrid. They know its impossible to do the Astrid part because shes dead, but Anna ruling Arendelle still had a chance. They get Anna to rule Arendelle rightfully, although they try to do it so well that Hiccup would be happy too. But Elsa still exists, stuck inside the Night Fury unable to do anything until she is freed by the way Anna thinks so, but she finally realizes that Hiccup won't be happy until she comes back. The Night Fury Elsa had bred with Toothless and now Toothless wasn't the only Night Fury, which made Elsa feel more content. Elsa frees herself from the Night Fury, which now shoots ice and snow instead of plasma, and finds Hiccup and Anna and have the greatest life that is possible.