The Monster of the Amber-Slavelands is a strange Sea Dragon that lives in caves under the Amber Slavelands. The Slavelands are alternately exposed red sands, but are fully covered by the sea when the tide comes in. This is most likely why it is classified as a Sea Dragon.
The most singularly strange feature of the Monster of the Amber Slavelands is the location of its eyes. It has hollow depressions on its head where we would expect eyes to be. Instead its red eyes are located at the very ends of its fingers.
The Amber Slavelands Monster is unknown to Hiccup when he first encounters it. He uses his knowledge of another ground-dwelling solitary dragon, the Burrowing Slitherfang, to infer behaviors and traits of the Monster of the Amber Slavelands. His comparisons prove to be correct, and help him escape this dragon's clutches.
- "Fifteen feet of well-armed, muscled dragon. Ten eyes. Huge claws. An interesting snaky aspect that suggested it might be related to a Slitherfang, which also lived under the sand. ... Hiccup's only chance was to hope that this creature really was a primitive relation if a Slitherfang and to use his knowledge of Slitherfangs to fight it."
- ―How to Seize a Dragon's Jewel
Hiccup also notes the Monster of the Amber-Slavelands has a long prehensile tail, can unhinge its jaw like a snake to swallow prey, and most importantly - has a weak spot in its skull in the middle of its forehead.
The Monster of the Amber Slavelands has a very high temperature fire breath.
These dragons are able to speak Dragonese.
The Incomplete Book of Dragons indicates the Monster of the Amber Slavelands has excellent eyesight as well as X-ray vision and a hypnotic gaze. It can have more than one head and is considered a chameleon, most likely because it can blend in with the sands to snatch prey.
The Slavelands Monster can lift up its hands above the surface of the sands (at low tide of course) like a periscope, and both see and snatch a victim. It will then drag its prey through the sands where commonly it may suffocate. Any prey still alive may be eaten right away or encased in glass to save for later.
The Monster of the Amber Slavelands forms extensive caves and tunnels under the sands and sea. It takes advantage of the sands' properties and the high heat of its flames and essentially makes glass walls and pillars, some of which hold its still-live victims. After traveling through the sands with a victim, it will punch through its cave wall to enter, then rapidly reseal the opening before continuing with its dinner.
Hiccup infers that this Monster would like to keep its burrows clean, as a Burrowing Slitherfang would. Therefore already dead prey would fowl up its home, and should be eaten right away to avoid spoilage (as opposed to keeping a live victim for eating later). Like Slitherfangs, the Slaveland Monster also swallows its prey whole. This is after covering in slimy mucous or saliva to help its passage into the digestive tract.
This dragon plays a central part in Book 10. Hiccup is a slave searching for the Dragon Jewel in the Amber Slavelands. He is also looking for a missing Fishlegs. He gets snatched by the Monster of the Amber Slavelands and must use his dragon knowledge to free himself, Fishlegs, and get back to the surface.
The Monster of the Amber Slavelands is discussed in this reference book, and is featured in the Dragon Key at the back of the book.
- It has been speculated that the franchise dragon the Sandbuster may be based on the Monster of the Amber Slavelands.