According to human demonologists, he had power over 30 legions of evil horses, and was said that "He takes away the sight, hearing and understanding of any person under the conjurer's request, and steals money out of kings' houses, carrying it back to the people. He also steals horses and everything the conjurer asks. Shass can also discover hidden things if they are not kept by evil spirits."
The Dark Legion in general was known to be relatively under developed as cavalry force, focusing instead in infantry, and often relied on vassals and allied cavalry, aside a small cavalry force that supported each legion, being Shass one of the first and few renown cavalry commanders of the Dark Legion.
As such, often his forces served as a vanguard, scouting, or protecting the advancing forces of the legion, which could originate the idea of him taking sight, hearing and understanding of the enemies of the legions, and his ability to discover hidden things, while the part of being a thief of horses could be due the requisitions of his legions of mounts of diverse types.
The preferred known forms of Shass was as a stork, or a stork-man, often keeping some avian features in his diverse forms.