I thought they would do this, releasing the film in december of this year. It's been a year after Season 2 and the cliffhanger, so everyone had the change to catch up and had to wait a year for it. Really wondering how they will portray it. Don't think they will adopt the book in its entirety because they are going to release a Season 3 so it wouldn't fit.
And i'm really curious how they will add David and Frida in to the story. They are not present in the book, but i can't believe they leave them out of this after being two important characters in the show. I just hope they won't repeat them what they did in S2EP13. Going after Hilda and her mum to find them. We have seen that. Would be funnier if Johanna lies to them, but they find out and Johanna refuses and doesn't want their help. Frida ignores her and decides to follow Johanna and uses her magic to help her, without Johanna noticing at first. David coul have a story that he is to afraid and doesn''t want to go and so stays behind. He regrets it later (thinking of Hilda who is brave and would help him if he needs it) and decides to find her. So he wonders alone and is actually the first one to find her. It makes him brave, it's character deveolpemtn because he has to conquer his fears of the trolls and set aside his fears to help Hilda. Later Johanna discovers that Frida has helped her and is with her and together they find Hilda and David with the trolls.
Like i said, i don't want to see a subplot involving David and Frida together and searching. We have seen that in the episode The Stone Forest that ended with the cliffhanger that is going to be resolved in this movie. I hope for a better and different subplot for them, especially for David. I just hope they are in it. Not only at the end of the start, but troughtout the film. Because they weren't in the book.
I think the film will also have a different ending and that they will save the ending from the book for the final of Season 3. It would make sence to do this, because if the use the book ending for the film, what will and do they have to tell in Season 3?