Grimbeard's Monstrous Strangulator

Grimbeard's Monstrous Strangulator is a dragon character that features prominently in How to Be a Pirate.

Early Life
Grimbeard's Monstrous Strangulator was taken as a baby by Grimbeard the Ghastly, a famous Viking ancestor of Hiccup. Grimbeard placed it with a vast store of his treasure in the Caliban Caves in the dark to grow and protect the treasure. It survived in the dark loneness, sending its tentacles into the surrounding cave system and snatching other dragons to eat, for the next 100 years.

Encounter with Hiccup
Hiccup, Fishlegs, Alvin the Treacherous, and Toothless get trapped on a sinking ship, but are able to swim into the Caliban Caves from under the water. They have breatable air. The group stumble into the cavern full of treasure, not knowing the Monstrous Stangulator is there under it. Alvin and Hiccup swordfight, disturbing the creature. Its tentacles grab Alvin and eat him alive. It also grabs Hiccup. However, Hiccup is able to communicate with it via Dragonese. He appeals to the dragon's sense of vanity, and tricks him into stabbing himself with his poisoned tail spike. Grimbeard's Monstrous Strangulator describes the process of poisoning, and finds he himself shows the symptoms. His brain explodes.

Appearance
Grimbeard's Monstrous Strangulator is a huge tentacle creature with a venomous tail. It is at least partially transparent, and its digesting food can be seen. Other parts of it are a lardy-looking white.