Fossas are a cat-like species related to the mongoose that are the top predators of the island of Madagascar. Many of the natives in Madagascar fear this predator and often tell myths about how it kills people.
In Malagasy folklore, the fossa seems to occupy a similar niche to the wolves in European folklore. It is considered to be a greedy, aggressive and wicked animal that will steal piglets and chickens as well as small children who wander too far into the forests. It is also considered taboo to eat the fossa, as they are reptured to rob graves and eat the bodies of ancestors. Nevertheless, fossas are sometimes taken as bushmeat. According to the local legends, they can also kill people with its farts and turn them into zombies by using its poisonous lick before disembowling them. It is told by the local people that they can extinguish campfires and will kidnap babies from their cribs at night.
Like the aye-aye, the fossa is often feared by many natives and is therefore depicted as an evil creature that steals others foods and kidnaps children while sneaking into their homes at night. Malagasy folklore often exaggerates the ferocity of the Fossa, claiming that it will prey upon cattle, or even humans. Parents often tell their children "Be good, or the fossa will get you", or worse, they might be reincarnated as one.
A possible reason why people fear the fossa and portray them as malevolent animals is because the first settlers may have encountered the extinct giant fossas living on the island, that had the strength of a lion and may have preyed on humans.
Reality
As a result of the natives' fears regarding these extraordinary predators, they are killed whenever they prey on chickens and their habitat is being destroyed by humans for farmings. This led to the species' endangerment and conservation efforts to protect them.
In fiction
The fossa is depicted as an antagonist in DreamWorks' Madagascar franchise. They are shown to terrorize the lemurs and attempt to eat them. They hardly resemble their real-life counterparts in everything but basic shape and rarely speak in the film. When they do speak, they put "fossa" in front of every word (ex: "Fossa hungry, Fossa eat."). They are terrified of Alex due to him being a lion and being much more physically powerful and intimidating. In the end, thanks to a setup performed by his friends and the penguins, Alex scares them away making sure that the fossas never bothered the lemurs ever again.