Legend of the Boneknapper Dragon (16:33)
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This came out in October 2010, and apparently it aired on Cartoon Network the day before it was released on DVD, so it might be more appropriate for me to list it in my TV specials section instead of my short films section, but I'm pretty sure I only ever saw it on DVD. But... I'd rather list it here.

Gobber believes his house was set on fire by a dragon called a Boneknapper, which no one (except Fishlegs) believes even exists. When Gobber sets out to find the dragon, Hiccup and his friends go along. Gobber tells them all a series of stories about his encounters with the Boneknapper over the years. (We see his stories in traditional animation, which I found a neat contrast to the CGI of the scenes set in the present.) Of course the Boneknapper eventually shows up and everyone realizes Gobber had been telling the truth all along (though there are some elements of his stories that are still pretty hard to believe). I don't want to give away the ending, but... the whole short film is pretty funny.

Gift of the Night Fury (22:11)
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In November 2011, another pair of DVDs came out, sold as a package deal. The main one is "Gift of the Night Fury," which is definitely my favorite of the HTTYD short films. The Vikings of Berk are about to celebrate a holiday called Snoggletog; this will be the first time they've celebrated with dragons as their friends instead of enemies. However, all the dragons suddenly leave unexpectedly, and no one has any idea where they're going. This makes everyone sad or whatever. I don't want to reveal what's actually going on, but Hiccup will find out. Meanwhile, Astrid tries to invent new traditions to cheer everyone up... though it kind of backfires. Still, everything turns out great in the end. Definitely an amusing and touching story. And the deleted scenes were good, too.

Book of Dragons (17:37)
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The other DVD in the package is "Book of Dragons," in which we learn a bit about some of the different types of dragon, including all the ones we've seen before and a few new ones. We also learn about Bork, the first Viking to keep records of what he learned about different dragons. This featured some traditional animation similar to that in "Legend of the Boneknapper". It was okay, but not much of a story, really.

Dawn of the Dragon Racers
I haven't seen this.