One of the stranger beasts of the Lower Planes, and one of the few beasts to not be of fiendish origin or direct influence, the terlen is a danger to any travelers both within the seas of the lower and along its coasts. As a relatively recent transplant from the Prime Material, little note has been given to this aquatic beast as compared to many, but it's managed to adapt quickly to its new environs.
Much as the egarus or the quill, the terlen is a mortal transplant taken hold in the waters of the Lower Planes. This vicious predator descends from a similarly-vicious creature known on its homeworld as a terl, an aerial barracuda noted for its devastating shriek and its control over ice. Its odd nature and abilities being quite intriguing, it was brought to Carceri by some unnamed figure centuries hence, to study and breed. Those initial beings escaped their captivity, however, making their way into the waters of Othrys.
While any number of creatures are known for having transformed over the generations upon their introduction to the planes, these beasts seem to have been especially mutable, barely recognizable from their origins. From Othrys, they spread onwards and outwards, and within hardly a century they were reported all across Carceri, Gehenna, and the Gray Waste.
Terlens are a carnivorous, predatory species, feeding on prey both in water and in air. Equally dangerous in both realms, these long, eel-like fish are capable of projecting themselves into flight through a combination of their broad pectoral fins and a natural telekinesis, with no trouble breathing or surviving in either environment. They can even travel on land if need be, though incredibly awkwardly, writhing like a snake with much less success.
Terlens hunt in small schools and feed on animals of all sorts; while they tend to hunt smaller, less dangerous prey such as fish, birds, and some small reptiles, some desperate packs will hunt mortals, one another, or even some lower castes of fiend. Unlike many predators, they prefer to hunt via hit-and-run tactics, harrying their quarry with quick, stealthy strikes, withdrawing to a safe distance, and striking again some minutes later. These attacks wear their quarry down gradually, and when they finally collapse, the terlens move in to feast.
Nomadic creatures in a realm of constant danger, terlens hold no particular hunting territory or lairs, instead constantly migrating to find new sources of food. As they hunt out or are driven away from one spot or another. This includes reproduction; come mating season, terlens will lay a clutch of 50 to 100 eggs in a muddy pit out of the water. Only perhaps five to ten of these eggs will survive the following 3-4 months, and after hatching, terlens seek out others of their kind through harsh, resonating cries above-water and pheromones beneath. Terlens reach their full seven-foot length after a year of growth, and under best conditions can survive for up to 30 years.
Terlen are long, eel- or barracuda-like fish with sandy gray skin covered in thin, silky vestigial feathers; a remnant of their material realm biology all but shrunk to nothing, these feathers today are more an aid in camouflage than an aid in flight, able to shift the apparent coloration of their bodies to better blend into their environment. Their pectoral fins are more akin to a bat's wings, a translucent gray membrane spanning upwards of four feet when fully extended and aiding in their maneuverability both in air and in water. When need be, they can also be folded against the body, providing greater speed underwater or (when rarely necessary) allowing for their awkward slithering movement on land. Their mouths are, much like a shark, filled with three layers of cartilaginous teeth, constantly being replaced over a terlen's lifetime.
- Fiend Folio (3e), pp.174-175
- Gamma World, pg.26
- Planescape Monstrous Compendium II, pp.114-115