A Monstrous Strangulator is a dragon species first featured in How to Be a Pirate.
A Monstrous Strangulator is a bizarre, tentacled dragon. It has a pair of wings and small legs that are, for the most part, non-functional. It is transparent in color, though the tentacles can be white like uncooked fat. This transparency of the body allows the bodies of the creatures it ate to be seen as they travel through the digestive system. Strangulators also have a spike on the end of their tails that resemble a hypodermic needle with which to inject a clear green toxin.
Though classified as a dragon, a passage in How to Be a Pirate is suggestive of the Monstrous Strangulator being a dragon-like creature.
The tentacles of the Monstrous Strangulator excrete a slimy white-grey mucous that is very malodorous.
The spike at the end of its tail injects a venom into its victim. The effects of a Monstrous Strangulator's venom are quite spectacular. First the affected part of the body stiffens; then it turns green; and then the entire nervous system explodes.
Monstrous Strangulators are able to speak an ancient form of Dragonese.
Despite being able to speak Dragonese, a Monstrous Strangulator's brain rather small and cannot concentrate on both speaking and monitoring all its tentacles. Because of this, they can be tricked, allowing escape.
Strangulators live in burrows and caves, never coming out into the sunlight.
Though armed with poison, Monstrous Strangulators most often dispatch their prey by strangling them with their tentacles. They capture prey by reaching their tentacles far out into the surrounding cave system and catching anything that stumbles across them.
A Monstrous Strangulator appears in the second book when Hiccup, Fishlegs No-Name, and Alvin the Treacherous come across one guarding Grimbeard's vast treasure under the Isle of Berk. The Monstrous Strangulator eats Alvin alive.
The Monstrous Strangulator is detailed in this reference book.