Experimenting with the Dragon Eye allows Fishlegs to find the location of Dark Deep, the ancestral home island of the Gronckles. Upon landing there, they find the island has been taken over by a massive new dragon dubbed as the Catastrophic Quaken. Its dangerous behavior forces the other Gronckles to leave and seek refuge on Dragon’s Edge, much to everyone's dismay. Determined to win back Dark Deep for the Gronckles, Fishlegs allows Snotlout to train him in fighting dirty behind Hiccup's back in order to beat the Quaken and drive it off.
Tropes:
- Attack! Attack... Retreat! Retreat!: Once with Hiccup and Fishlegs, then again later with Snotlout and Fishlegs (although Fishlegs ultimately stays).
- Befriending the Enemy: Meatlug chooses to make friends with the Quaken instead of fighting it. It works, resolving the conflict it had with the other Gronckles.
- Catapult Nightmare: Fishlegs wakes up screaming from a nightmare where the Quaken in trying to run him over while Snotlout is taunting him.
- Indy Escape: Hiccup, Fishlegs and the Gronckles fleeing from the rolling Quaken in a tunnel. At first they think it's an actual boulder and they manage to dodge it, but then the "boulder" stops and rolls up the slope, to their dismay.
- Pun: Courtesy of Tuffnut. Leads to Lame Pun Reaction from the rest of the group.Tuffnut: We got off to a rocky start!
- Rolling Attack: The Quaken's main mode of attack is to curl up into a ball and roll over anything in its path.
- Screw This, I'm Outta Here: Snotlout tries to retreat after he sees how big the Quaken is, but Hookfang wouldn't let him abandon the others.
- Shockwave Stomp: Although not done by stomping, the Quaken can attack by curling up while flying and dropping into the ground with extreme force. And the shockwave doesn't just expand in the ground, but also in the air around, with enough strength to destabilize other flying dragons.
- Technicolor Fire: Technicolor lava to be exact; Fishlegs experiments with different kinds of rock for Meatlug's lava breath, resulting in lava colored blue, green, and purple alongside the usual orange.
- Training Montage: One in which Snotlout teaches Fishlegs and Meatlug how to fight dirty and aggressively.
