How to Train Your Dragon: Homecoming, on NBC
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This first aired in 2019, but I didn't see it until 2021, on Hulu. Not really a Christmas special, instead it's based on a winter holiday called Snoggletog, which was first introduced in the short film Gift of the Night Fury. It's set ten years after the main part of How to Train Your Dragon: The Hidden World (after humans and dragons decided to live apart from each other), but shortly before the movie's epilogue.

Hiccup and Astrid are married, with two children, a girl named Zephyr and a boy named Nuffink. Hiccup likes to tell them stories about dragons, but Zephyr believes dragons were monsters, not friends. Hiccup decides the village should put on a Snoggletog pageant which shows the story of how humans and dragons became friends. Gobber writes the script, which credits his old friend Stoick with having befriended Toothless, instead of Hiccup. Meanwhile, Toothless is missing Hiccup, and draws a picture of him in the sand. Later that night, his three offspring fly to New Berk, where they watch the humans in secret. Toothless and the Light Fury go after them, and Toothless ends up becoming part of the play, though no one but Zephyr notices.

That's pretty much the whole story, and it leads directly into the epilogue of the movie. It was fairly amusing and I definitely enjoyed it, but not nearly as much as the movies.