When Alvin the Treacherous captures the Skrill, Hiccup, Ruffnut, and Tuffnut go undercover to discover that a truce is in the process of being formed between the Outcasts and the Berserkers to invade Berk with the Skrill as their weapon. Dagur is giving Alvin the support of his vast fleet in exchange for the Skrill, but the truce is uneasy. The trio must now flee to release the Skrill from their control before the truce can be settled.
Tropes
- Bavarian Fire Drill: How Tuffnut convinces enemy soldiers he's one of them.
- Becoming the Mask: Played for Laughs; after going undercover, Tuffnut forgets whose side he's on while reporting to Hiccup.Tuffnut: The plan is to smash those dirty Berkians to pieces, with both fleets! It's gonna be awesome.Hiccup: Uh, you do realize, we're the Berkians?Tuffnut: Oh, right. Still gonna be awesome!
- Didn't Think This Through: Tuffnut's tree disguise, not only can he not see what he's spying on, but bark beetles get in his pants.
- Disney Villain Death: Alvin is presumed dead after jumping into water that was electrified moments later. Of course, they Never Found the Body.
- Evil vs. Evil: Dagur and Alvin inevitably come to blows by the end of the episode. Dagur wins.
- Foil: Hiccup and Toothless vs Dagur and the Skrill; the former are best friends, trust each other to death, and Hiccup rides Toothless. Meanwhile Dagur intends to enslave the Skrill, sees it only as a weapon, and uses specialized reins to hang underneath it like he's parasailing.
- Hall of Mirrors: Hiccup uses his and Toothless's reflections in the ice cave to trick the Skrill into stunning itself long enough for the twins to refreeze it.
- He Didn't Make It: Ruffnut says this about Tuffnut when Hiccup asks where he is. Turns out he's just hiding in a tree.
- Hoist by His Own Petard: Dagur is defeated by stepping into a puddle while he's holding the Skrill's reins, and gets electrocuted for his trouble.
- Most Definitely Not a Villain: Inverted, Tuffnut pretends to be "Berserker Buffnut" in order to infiltrate Outcast Island.
- No One Gets Left Behind: Why Hiccup stays out looking for the twins after they went MIA in the last episode.
- The Unintelligible: Anyone hit by lightning, though special note goes to Mildew, who is rendered unable tell his allies that "Buffnut" is actually from Berk.
- Villain Team-Up: Alvin and the Outcasts, Dagur and the Berserkers, and Mildew have all teamed up and are planning to use the Skrill to destroy Berk.
- With Catlike Tread: Tuffnut's infiltration, in which he falls off his perch and lands in the middle of enemy soldiers.
- You Have Outlived Your Usefulness: Alvin and Dagur intend to do this with each other. Dagur is the one who succeeds.
