Similar to large earthworms, psurlons had long pink tubular bodies with two arms and many legs that were also long and tubular in shape, ending in sharp claws. Their entire bodies were marked with faint rings. In the place of a head, the creature's body ended in a circular maw filled with harp teeth, surrounded by equally spaced visual organs capable of darkvision.

Powerful telepaths, psurlons could communicate with creatures through thoughts, and their innate psionic abilities rendered them almost immune to spells such as sleep and conditions such as charmed. Their senses were well adapted to life in the underground darkness, allowing them to perceive vibrations, objects, and creatures without relying on sight. 

Psurlons were naturally distrustful and ill-tempered. Clever, cruel, and deceitful creatures, they hated all humanoids and went to great lengths to kill or drive them away from their domains. Thy also relished fomenting discord among other peoples, manipulating and deceiving leaders and occasionally helping furthering evil goals. 

Despite being capable of using their claws and teeth, psurlons were not particularly strong physically, so they relied mostly on their psionic abilities during combat. They were capable of confusing and controlling their opponents via their innate abilities. More powerful psurlons could also cast stronger spells, known as elder psurlons. 

Although typically solitary creatures, psurlons occasionally organized themselves in groups known as "clusters". Living in the deep Underdark, psurlon clusters kept large numbers of psionically dominated slaves and thralls. They were known for convincing goblinoids and gnolls into joining their ranks on occasion.