When Hiccup is making Toothless a tail that will allow him to fly on his own, Astrid says "you tried that once before; he didn't want it." This refers to the Dragons holiday special, 'Gift of the Night Fury.'
In September 2012, 20th Century Fox, the studio's then-distributor partner, and DreamWorks Animation announced the film was originally going to be released on June 17, 2016. In September 2014, the film's release date was pushed back a year from its original release date of June 17, 2016 to June 9, 2017. In January 2015, the release date was pushed back a year from June 9, 2017 to June 29, 2018 following DreamWorks Animation's corporate restructuring and lay-offs. On June 18, 2016, the release date was moved up from June 29, 2018 to May 18, 2018, taking the release date of Warner Animation Group's The Lego Movie 2: The Second Part. On December 5, 2016, the U.S. release date was pushed back from May 18, 2018 to March 1, 2019. The release date was moved up for a final time from March 1, 2019 to February 22, 2019, taking the slot of The Turning, a live-action DreamWorks film which in turn was pushed back to January 24, 2020. Which makes How to Train Your Dragon: The Hidden World have a total of six release date changes.
Unlike How to Train Your Dragon 2 (2014), the third film will have a subtitle, ''The Hidden World'', instead of being numbered. The second film was at one point subtitled ''Secrets Of The Ice Cave'' before being shortened to just ''How To Train Your Dragon 2''.
Months before the films release, Amazon and other websites released preview pages for the book tie-ins to The Hidden World. Some of the pages in the books spoiled major plot points of the movie. The pages have since been taken down.
This film was originally going to be released in 2018 as one of the last DreamWorks movies to be distributed to 20th Century Fox but was moved to 2019 as the first DreamWorks movie to be distributed to Universal Pictures.
On April 17, 2018, a little less than a year before this film's release, the title was confirmed to be How to Train Your Dragon: The Hidden World rather than simply How to Train Your Dragon 3. However, this is the original title, as the film was released in most countries as How To Train Your Dragon 3.
The trivia items below may give away important plot points.
Grimmel reveals the reason why Toothless is the last Night Fury: It's because he hunted every other single one: This explains why in the first film, the Book of Dragons had nothing on Night Furies. However, in the Hidden World, several surviving Light Furies can be seen among the dragons.
In earlier drafts of Dragon 3, Drago Bludvist was planned to reprise his role as the movie's main villain, and be redeemed by the end of the story. In a recent interview with Cloneweb, it was revealed that Drago's redemption, and overall return, was scrapped halfway through the movie's production.
Astrid's hairstyle and clothing changes over the course of the films. In the first film, she wears her hair in a tight braid and wears clothes covered in armor and spikes. These symbolize her initially harsh and overly aggressive personality. In the second film, she wears a looser braid and her clothes have a noticeably softer appearance. These show how Hiccup's kind and loving nature has influenced her. In this film, her hair is now in a half-braid and her clothes are more sleek and feminine. These mirror her maturity and full change of heart.