The Fireworm Queen has come to Hookfang and Snotlout looking for help, not from the Dragon Hunters but from an invasive dragon known as the Cavern Crasher.
- Convection Schmonvection: The riders should have been roasted alive when the Crasher set that trail of slime on fire in the cave — instead, as long as you don't touch the flames, you're okay.
- Covered in Gunge: The Cavern Crasher sprays its sticky mucus at its targets, which then becomes highly flammable, causing them to explode if they get hit by the Crasher's fire or try to breathe any of their own.
- Eats Babies: The Cavern Crasher eats the eggs or hatchlings of the dragons whose caves it steals. The Fireworm Queen doesn't want her brood eaten, which is why she wants Hookfang to help her.
- Limit Break / Combination Attack: Hookfang and the Fireworm Queen pull one off, combining their fire jackets into a corona like fire blast. It burns away the Cavern Crasher's mucus, causing it to lose its edge over them.
- No-Sell: The Cavern Crasher is immune to fire, and can avoid being hurt by a cave in by collapsing its skeleton.
- The Cuckoolander Was Right: Wondering how the Cavern Crasher is moving around the cave so quickly, Tuffnut suggests it slipped through the cracks. While this is dismissed as a silly notion, it does actually collapse its skeleton and use its mucus to pass through small cracks.
- This Is Something He's Got to Do Himself: Snotlout insists he has to help the Fireworm Queen himself, and leaves the group at the first opportunity he gets.