It's been months since the Viggo incident and he's still nowhere to be found. Desperate to find him, Hiccup sets out on a reconnaissance mission alone, but falls into a Dragon Hunter trap and is shot down. Stranded by himself on a desert island with Toothless out of commission, Hiccup finds an unlikely ally in the form of Dagur.
- Bored with Insanity: Dagur has been stranded on a desert island since he left Viggo. The months alone with his thoughts has changed him somewhat.
- Character Development: Dagur's time in isolation has caused him to rethink his entire life, before he was a warmongering Berserker with an army and a grudge, free to do as he desired with no consequences. Now, he has a sister to protect, no home to fall back to and no friends to call his own. His entire purpose now is to find and protect Heather, and make Viggo pay.
- Doomed by Canon: After developing dragon armor for most of the last season, we get our first signs of why we don't see Armored Dragons in How to Train Your Dragon 2; the dragons just consider it too uncomfortable.
- Drama-Preserving Handicap: The hunters wound Toothless with a Dragonroot arrow, which seems to cause an adverse reaction to him as opposed to what it does to the other dragons. This puts him out of action for the majority of the episode, requiring Hiccup to begrudgingly accept Dagur's assistance.
- Enemy Mine: Between Dagur and Hiccup. The former insists he has reformed over the past few months of isolation, the latter refuses to take him at face value.
- Find the Cure!: Dagur helps Hiccup find the ingredients for the antidote for dragon root.
- Go Mad from the Isolation: Hiccup believes this has happened to Dagur, which is impressive since he was already bonkers to begin with, but ultimately defied in that it has given him some much needed clarity instead.
- HeelFace Turn: During the months between Viggo's attack on the riders and meeting up with Hiccup, Dagur realized just how much worse Viggo is compared to him and decided to switch sides.
- Mysterious Protector: Dagur before Hiccup learns who's been taking out all the hunters behind his back.
- Properly Paranoid: Hiccup. Since Dagur is clearly a few yaks short of a herd, Hiccup really doesn't want to trust him, even though the evidence to the contrary mounds up around him. It isn't until Dagur appears riding Toothless that he lets go of the paranoia.
- Playing Possum: Hiccup finds a Dragon Hunter ship that appears to have been attacked, only for it to be a trap.
- Tempting Fate: Astrid tells Hiccup not to leave on his own in case he gets into trouble, but he ditches her to go alone anyway and immediately gets into trouble.
- As a bonus, Hiccup foregoes Toothless's armor as it allows him to be stealthy on a recon mission, then encounters enemies with Dragonroot arrows.
- Whole Plot Reference: The hero, separated from his team, is pursued by enemy archers while trying to Find the Cure!, only to be saved by a Mysterious Protector, leading to an Enemy Mine situation. It's the Avatar: The Last Airbender episode "The Blue Spirit" with a happy ending.