Leucrottas, sometimes called ugly killers, were hideous monsters that lurked far from civilization bullying and torturing wild animals. They were frighteningly intelligent creatures that used their vocal imitation abilities to lure the unsuspecting, animal or humanoid, into their simple but effective traps.
Seemingly patchwork in bodily structure, a leucrotta's form was composed of the parts of a wide variety of animals. Their heads were low-slung, wedge shaped and similar in appearance to that of a giant badger. Their body was 9 ft (2.7 m) long and seemed to be a cross between a stag and a hyena. Deer-like legs ending in cloven hooves were far more concrete in their resemblance, but nonetheless made it impossible to distinguish between the tracks of a leucrotta and a stag. Ending the mismatched creature's form was a tufted lion-like tail. Male and females were indistinguishable without an in-depth examination. The laughter of a leucrotta was made distinctive, as it was a cross between hyena and human.
By themselves the patchwork features of leucrottas did not make their hideous appearance inevitable. In fact, a leucrotta could be a handsome, and even a humorous looking beast if those were its only traits. Instead, the horrible appearance of the leucrottas was a result of their more off-putting characteristics, such as their glowing red eyes, constant drooling, and jagged bony ridges in place of teeth. Other eerie features were their oily, putrid, skin that was colored a motley of black, gray, and brown. The notably noxious stench that hung off their bodies was topped only by their awful breath, corrupted by a combination of digestive fluid and carrion. A pink dog-like tongue further contributed to their hodgepodge physical structure. Their generally ghoulish appearance was furthered by their skeletal form and lack of close-cropped fur. 
The mind of a leucrotta was clever and cruel, reveling in murder, deception, and meticulous torture. Sadistic bullies of the wilds, leucrottas drew out their kills as long as possible, even when not hungry. Indeed hunger was not the motivating factor behind the leucrotta's hunting, as it was more out of a desire to inflict pain. Leucrottas were prone to overhunting even when well-fed, resulting in piles of carrion that only evil-aligned scavengers dared to touch. When not hunting for food they did so for sport, invented killing games to pass the time and mimicked the noises of some of their longest-living victims. Territory defense was not a particular concern of a leucrotta as they wandered about a given area and would leave it without hesitation if dangerous predators, localized disasters or absence of prey became apparent. They were not fully nomadic and did prefer to frequent territory they were familiar with, but simply saw it as a convenience.
Being cruel and torturous beasts, one would expect leucrottas to go after humans, which would be an easy target in most circumstances. However, leucrottas were smart enough to realize the communal nature of humanoids meant that killing one would provoke the ire of others, making it a dangerous tactic. If a leucrotta did not believe such an entity had allies that would avenge it however, it would happily devour isolated humanoids, as humans were among their favorite food. Normally they attempted to imitate the noises of a small child or a member of the opposite gender, and failing that a known friend. They did not possess an insane level of intelligence, but their propensity to wickedness gave them a sly cunning not present in non-evil entities of similar intellect.
One of their nastier tricks was the theft of a pilgrim caravans' torches. After devouring a few travelers, a small group of leucrottas used their torches to light nearby brushes and wall torches in order to make a deserted keep seem inhabited. They then used their deceptive powers to convince a larger caravan into entering the keep, and splitting up before devouring those they could and chasing after the stragglers. Observation of common expressions and news was also performed by leucrottas that lurked along the fringes of civilization during the night. Once, a leucrotta that stumbled upon on a thieves' den used the vocabulary it overheard to lure thieves into its traps, returning every few weeks for many years until finally being slain.
Leucrottas often lurked along roads and near habitations by night, learning information about humans who lived in the area or were passing through the wilderness. A more common ploy executed by a leucrotta was the imitation of an injured individual to lure the good of heart to their doom. While none of their tricks were particularly sophisticated or overly complex they were made all the more effective by their relative simplicity. Leucrottas found the mindsets of humans puzzling, as they treasured secrets and gemstones over food.
Stalking came easily to leucrottas, as their strong sense of smell and difficult to distinguish tracks made them both excellent in pursuit and stealth. They often attempted to make the task easier by viciously savaging prey before stalking them as they bled out. Leucrottas went on the prowl under the cover of night or masking terrain before rushing out at prey and tearing away at them with their jagged jaws. Despite their massive size they could move as fast as a normal-sized warhorse. Rather than finish off victims one at a time they disabled one opponent before lashing out at the next. The jaws of a leucrotta had steel plates as strong as adamantine in place of teeth, capable of ripping the armor and flesh of a well equipped knight.
Their equine hooves were also dangerous, able to bring down their full weight upon fallen victims or kicking opponents from the rear before making sudden retreats. They were known to carry a mild resistance to poison and diseases. While the foul stench of a leucrotta would normally give it away, leucrotta possessed the ability to mimic the noises of humans and animals. All imitations were done with an equal amount of skill by adult leucrottas and the only way to improve this ability was to learn more about their targets to craft more convincing illusions. So innate was the evil of a leucrotta that many were reported to be immune to the effects of charm and compulsion magic.
Leucrottas possessed enough forward planning skill to collect gemstones despite having no personal use for them, as they could be used as trap material or as bargaining chips. Those forced to live nearby leucrottas were constantly wary of raiding, never spoke to anyone they couldn't see, and kept careful eye on pets like dogs, that were despised by leucrottas for their alerting habits.
Most leucrottas preferred to work in small groups of 2-4 with other members of their race, though some also hunted alone. They did not possess names and identified each other by individual odors. Packs were the only societal structure they possessed, recognized by a unique combination of individual musks and with territory marked using their smells. Although their astonishing ugliness would lead many to deduce that leucrottas operated alone, and failing that only other members of their kind, leucrottas were varied in the creatures they cooperated with and could be found in many kinds of social structures.
Almost all beings shunned the leucrottas, and they were only worked with sparingly, with most beings actively seeking the destruction of the brutal creatures due to their wasteful behavior. Even druids, good or evil, loathed their existence and many thought their origins to be unnatural. Cooperation with other evil entities was only done by leucrottas for mutual gain, and only in the service of beings more powerful and ferocious than themselves. Such deals were based almost purely out of fear, and leucrottas would attack if a deal was no longer profitable and their former partners were at a point of weakness. Such teammates might include evil nagas, lamias, and powerful demonic forces. On rare occasions, other creatures of similar alignment would be allowed to join a hunt, although this might only last for a single excursion.
The one exception to the opportunistic backstabbing of leucrottas was when they dealt with gnolls. While the superior strength, speed and intelligence of a leucrotta could allow them to easily rule this was almost never their intent as it would be disruptive. Instead leucrottas served as bodyguards, advisers, and even mounts for the gnoll that was currently in charge. Gnolls likewise appreciated leucrottas, seeing them as a form of entertainment as they could mimic the cries of a suffering victim without the gnolls needing to seek them out. When victims were present, leucrottas were typically the ones to oversee the torture as their cautious cruelty let them drag out a kill longer than the bloodthirsty gnolls, who enjoyed watching a leucrotta work almost as much as personally enacting the torture.
It was often debated by sages whether or not leucrottas were intelligent or just cunning and talented, a mystery caused by the fact that very few intelligent species could stomach the thought of keeping any alive. The truth was that they were intelligent and even had their own "pantheon" of gods and goddesses, known as The Pack whom they worshiped fervently. The pack was led by the greatest and possibly first leucrotta, Toknana.
Male leucrottas were known to journey hundreds of miles to find suitable partners, but did not take permanent mates. The father did not take care of the young either, although they did stay around while the female was pregnant.
Calves were born live, alone or in a pair, fully capable of cognitive function and about the size of a bear. Two months after being born the mother would become more kill-crazed than normal, slaughtering anything nearby to provide food for her calf as the calf itself developed its mimicry. Young followed the mother for 4 months while learning to master their mimicry and hunting before leaving the mother after 8 months, presuming that the mother did not become pregnant 2 months after the first calf was born.
A leucrotta's lifespan was believed to be shorter than that of a human's.
Ranging from subtropical to subarctic, leucrottas could habituate many diverse biomes. Those residing in arctic regions had a thick layer of fat to shield them from the cold that blunted conventional weaponry. Most dwelt in hilly or mountainous places using their hooves to easily maneuver throughout rocky cliffs and ravines.
Deep within the depths of the Abyss were legendary leucrottas that resided in the Iron Wastes, far more powerful than their worldly counterparts. They were huge monsters with regenerative abilities an and immunity to frost, but a vulnerability to heavy heat.
There existed a type of leucrotta tainted with doppelganger blood known as a changesteed, that had a stronger craving for humanoid flesh and would transform into a rider's mount and take their place before attacking them when they were alone.
During Yeenoghu's first ancient incursion of the Material Plane, the hyenas who consumed his kills went through aberrant transformations, creating an assortment of bizarre and fiendish monstrosities. While most of these were gnolls, the second most common result was the leucrotta. Leucrotta foremost served the interests of the Ruler of Ruin when requested, but were keen to torment random beings if left unchecked.
Since then the leucrottas had worked under other demonic powers, such as Kostchtchie, Prince of Wrath. The demon lord saw a bit of his own mindset in their behavior and treated them like how a king treated his mastiffs, as hunting dogs and bodyguards that helped him in his demon hunts and that he fed his victims, whose armor crunched like paper under their fangs. Those of sufficient power in Kostchtchie's faith could call upon these pets whom he dubbed his hounds.
Between 1368 DR and 1372 DR an unprecedented numbers of leucrottas had been seen around Silverymoon and Everlund. In 1372 DR bounties had been paid for leucrotta ears in Silverymoon and Everlund for many years. Leucrottas were so renown for their malice there that the locals had turned its name into a swear word that meant; a good plan turned into a bad idea by terrible luck.
- Ed Greenwood (November 1984). “The Ecology of the Leucrotta”. In Kim Mohan ed. Dragon #91 (TSR, Inc.), pp. 16–17.
- Eric L. Boyd (June 2005). City of Splendors: Waterdeep. (Wizards of the Coast). ISBN 0-7869-3693-2.
- Jaleigh Johnson (September 2008). Mistshore. (Wizards of the Coast), p. 259. ISBN 0-7869-4966-X.
- Mike Mearls, et al. (November 2016). Volo's Guide to Monsters. Edited by Jeremy Crawford, et al. (Wizards of the Coast), p. 169. ISBN 978-0786966011.
- James Wyatt and Rob Heinsoo (February 2001). Monster Compendium: Monsters of Faerûn. (Wizards of the Coast), pp. 63–64. ISBN 0-7869-1832-2.
- Eric L. Boyd (June 2005). City of Splendors: Waterdeep. (Wizards of the Coast), pp. 136–138. ISBN 0-7869-3693-2.
- Doug Stewart (June 1993). Monstrous Manual. (TSR, Inc), p. 221. ISBN 1-5607-6619-0.
- Gary Gygax (December 1977). Monster Manual, 1st edition. (TSR, Inc), p. 60. ISBN 0-935696-00-8.
- James Butler, Elizabeth T. Danforth, Jean Rabe (September 1994). “The Great Gray Land of Thar”. In Karen S. Boomgarden ed. Elminster's Ecologies (TSR, Inc), pp. 14–15. ISBN 1-5607-6917-3.
- Ed Greenwood (November 1984). “The Ecology of the Leucrotta”. In Kim Mohan ed. Dragon #91 (TSR, Inc.), pp. 16–17.
- James Jacobs (July 2006). “The Demonomicon of Iggwilv: Kostchtchie: Prince of Wrath”. In Erik Mona ed. Dragon #345 (Paizo Publishing, LLC), pp. 29–30.
- Ed Greenwood (August 2006). Swords of Eveningstar. (Wizards of the Coast), chap. 6, p. 72. ISBN 978-0-7869-4022-6.
- Bruce Nesmith, Andria Hayday, William W. Connors (1994). “Domains and Denizens”. Ravenloft Campaign Setting (TSR, Inc.), p. 17. ISBN 1-56076-942-4.
- James Butler, Elizabeth T. Danforth, Jean Rabe (September 1994). “Explorer's Manual”. In Karen S. Boomgarden ed. Elminster's Ecologies (TSR, Inc), p. 8. ISBN 1-5607-6917-3.
- James Wyatt and Rob Heinsoo (February 2001). Monster Compendium: Monsters of Faerûn. (Wizards of the Coast), p. 64. ISBN 0-7869-1832-2.