Hills of Ash, they seem to live.
Anatomy & Morphology
Nobody has seen the creature that's supposedly hiding under the hills of ash, or died before they could tell their discoveries. the only thing we truly know about them is that they are moving hills with an mouth full of sharp teeth.
Ecology and Habitats
They only appear on the endless plains, making it one of the most dangerous areas on this place.
Dietary Needs and Habits
It eats everything living. but it prefers the ones capable of fear, it gets a kick out of that.
Perception and Sensory Capabilities
They can send some kind of Psychic pressure to the area around them, it makes mortals feel uneasy. The mortal thinks it would be attacked by some horrid creature and tries to lock itself in something, making it easy prey for the Dune.