The Thalassic Megathrust Dragon, also known as Trench Sleepers or Great Displacers, is a legendary species thought to date back to the earth's tectonic plates. With only about a dozen remaining, they are primarily regarded as myths due to their immense size and slumbering nature. These colossal creatures, measuring 400 to 600 feet long and weighing up to 150,000 tons, are distinguished by their pitch-black, blubber-like armor and unique features like shovel-like heads and parasitic barnacles.

Feeding on abyssal carrion and magma, they inhabit deep oceanic zones, exerting control over gravity and triggering severe earthquakes. Their communication occurs through subsonic rumbles, and they are known to have a solitary social structure. Each female reproduces every ten thousand years, laying eggs in subduction zones. Cultural lore depicts them as the causes of earthquakes, with significant impacts on maritime civilizations that live in fear of their awakening, often seen as a harbinger of catastrophe. Notably, the famous Great Displacer is said to be so large that its movements could devastate continents.