With Dagur holding Stoick the Vast hostage, and demanding Toothless as ransom, Hiccup has to Take a Third Option to rescue his father. That option: asking for Alvin the Treacherous's help.
Tropes for this episode include:
- Ain't Too Proud to Beg: Dagur for Hiccup's help when Alvin captures him in the climax.
- Anti-Climax: How Alvin describes the events surrounding his exile from Berk: during a skirmish, he defied orders, which led to "several casualties". Alvin seems to minimize what those casualties were.
- Badass in Distress: Stoick, as a hostage, though once he's free he punches out several Berserkers with his bare hands.
- Chekhov's Armory: Dragon Root, the Screaming Death, and Outcast Island's Whispering Deaths all come into play for Hiccup's plan to rescue his father.
- Easily Forgiven: Due to the necessity of an Enemy Mine, Hiccup forgives Mildew for being a traitor and Alvin for kidnapping him in the previous season.
- Enemy Mine: Hiccup with Alvin and Mildew to take down Dagur and give Alvin his tribe back.
- Explain, Explain... Oh, Crap!: The riders receive a message from Hiccup to lure the Screaming Death. They think to use Dragon Root, only most dragons compete over it. Fishlegs then points out that Gronkles are immune, only to realize that he's volunteered himself and Meatlug for the dangerous job.
- Godzilla Threshold: Hiccup knows very well he is doing this by releasing Alvin and trusting him to get onto Outcast Island without getting caught. A more literal example happens with the plan to draw the Screaming Death into the island.
- Hostage for MacGuffin: Dagur sends a ransom note demanding Toothless in exchange for Stoick's life. Astrid points out that it's a trap, since Dagur wants revenge on Hiccup as well.
- Idiot Ball: Alvin trying to force Hiccup and Toothless to use an underwater tunnel, while hovering mid-air. He could have easily damaged the rigging or tossed them all into the ocean.
- I Surrender, Suckers: Hiccup and Toothless allow themselves to be captured so as to provide a distraction for Mildew and Alvin to release Outcast Island's Whispering Deaths.
- Screw This, I'm Outta Here: Savage when he sees the tides turning against Dagur the Deranged.
- Well-Intentioned Extremist: The Screaming Death only wanted to reunite with its mother, who was on Outcast Island. When Hiccup saves its mother, SD roars in his face and flies away to unknown parts.
- What Happened to the Mouse?: We last see Mildew helping in the battle against the Berserkers. Next season, he's no longer anywhere to be seen on Berk. No hint of his ultimate fate or punishment for betraying his tribe is ever shown.
