One of the stranger beasts of the Lower Planes, and one of the few such beasts to not be of fiendish origin or direct influence, the terlen is a potential danger to any travelers both within the seas of the Lower and along its coasts. As a relatively recent transplant from the Prime, little note has been given to this aquatic beast as compared to other local dangers, but its oddities deserve mention.
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 obscure homeworld as a terl, an aerial barracuda noted for its devastating shriek and its control over ice. Its odd nature and abilities having intrigued a visitor to that world, a number of terl were brought to Carceri by said visitor centuries thence to study and breed as either a curiosity or a living weapon; surviving records are unclear on this point. Those initial beings escaped their captivity, however, making their way into the waters of Othrys where they quickly began to multiply in the unfilled gaps within that layer's ecosystem.
While any number of creatures are noted for having transformed over the generations especially quickly upon their introduction to the planes due to exposure to the metaphysical properties of pure belief, these beasts seem to have been especially mutable, barely recognizable from their origins. (Records seem to further indicate that this was a common property of beings of all sorts from this world, leading one to wonder what other known creatures on the planes today may have had similar origins.) From Othrys, they spread onwards and outwards, and within hardly a century populations of terlen were noted across all viable layers of 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 environments, these amphibious fish are capable of projecting themselves into flight through a combination of their broad pectoral fins and a natural telekinesis, able to breathe without trouble in both water and air. They can even travel on land if need be, though incredibly awkwardly, writhing like a snake with much less success.
A communal species, they hunt in small schools and feed on animals of all sorts; while they tend to prefer 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. (Indeed, the terlen seems to be growing more aggressive and more willing to strike against otherwise-dangerous quarries unprovoked, though whether this is the impact of the darker nature of the Lower imprinting itself on their essence or a simple response to the danger most in the Lower pose to any around them is yet unknown.) 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 region or another. This includes reproduction; come the annual mating season, terlens will lay a clutch of 50 to 100 eggs in a muddy pit or darkened treetop and press onwards, leaving the eggs to fend for themselves. 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, tracking their number through both scent and their harsh, resonating cries, the only remnant of their once-deadly sonic shriek. Terlens reach their full seven-foot length after a year of growth, and under optimum conditions can survive for up to 30 years.
Terlens are long, barracuda-like fish with sandy gray skin, smooth and scaleless, covered in thin, silky vestigial feathers that appear almost opalescent in the light. A remnant of their material realm biology, these feathers today give no help in flight, but provide a degree of camouflage; terlens are able to shift the apparent coloration of their bodies by adjusting the positioning of the feathers subtly 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 or (those rare times when 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