A Nightmare is usually purple or scarlet and possesses a long, snakelike neck and tail. Unlike some other breeds of dragon, it has no forelegs, and its ground-based locomotion is similar to that of pterosaurs; it can use its claw-tipped wings to "crawl" along the floor.
As it is quick to anger, the Monstrous Nightmare can be counted on to be the first to arrive and the last to leave in a fight. Its signature attack strategy, known as the "Fire Jacket," is to engulf itself in flames (from an external source or otherwise), resulting in an intimidating offensive and defensive maneuver similar in appearance to napalm or other gel-based incendiaries.
According to Gobber the Belch, the best way to engage a Nightmare is to clamp its mouth shut, leaving it unable to open its enormous jaws, much like a crocodile (however, the rest of the dragon is free to do whatever it wants).
By unofficial Viking law, only the chief, or the son of the chief, can own one. Despite this, Snotface Snotlout, the nephew of the chief, acquires one named Fireworm (How to Train Your Dragon), while Thuggery from the Meathead Tribe owns another named "Killer."
One is used as the last initiation test for the young Vikings before the Vikings befriend the dragons. Despite their vicious nature and fierce combat abilities, it is shown that a Night Fury can defeat it through a brief but brutal fight.
- "No dragon is more ferocious, or feared than the Monstrous Nightmare. This gigantic dragon has a long, snakelike neck and tail, and is covered in red scales and long sharp spines. The Nighmare's gigantic head and mouth can swallow Vikings whole. This dragon can attack any time of the day or night, from the air or on the ground. It is highly aggressive, and will never run from a fight. Its fire is thick and sticky, clinging to walls and running down hills like a flaming river. The Nightmare also has a nasty habit of setting itself on fire."
According to the trivia track on the Blu-Ray version of the movie, a Nightmare measures 69 feet in length.
"This red-and-black creature with a huge wing span produces a kerosene gel fire. “He is the most dragony of the dragons,” Sanders says, “but the thing that we like is that he is the most showy. We always felt he was the Mick Jagger of dragons. He’s a natural-born performer who comes out engulfed in flames because they can set themselves on fire.”"
Role in the series
A monstrous nightmare appears in the series as Stottrog's mount.