Peryton

Strange creatures with the jaws of a wolf, head and antlers of a deer, and wings and talons of an eagle, perytons are dreadful monsters. Their fur and plumage are dark, ranging from deep blues and purples to black. They live along mountainsides and in thick, dark forests. At night, perytons hunt, striking from dark corners of the sky. An innate knowledge of how shadows are cast allows them to always stay out of sight until they wish to be seen. It also allows them to change the shape of shadows they cast, using this ability to instill fear in their prey as they stalk. A peryton's preferred prey is marinated in fear before the kill; it will play with shadows and sound to build tension until the prey breaks down and succumbs to instinct. Before it strikes, the monster will unleash a piercing howl, a bone-chilling shriek that is something between an owl screech and lupine howl. It is only then, when the prey's heart is beating its fastest, that the peryton strikes. A peryton only consumes the heart of its victim, and it only hunts people. The jaws tear through the chest and pull out the hammering muscle. With an obvious delight, it gulps down the heart and flies off to stalk another victim. A single heart can sustain a peryton for an unnaturally long time, and it nay be a month or more before the monster needs to eat again.
Perytons are highly territorial, fighting for hunting rights near humanoid settlements. Battles for territory or during the rut can be gruesome affairs. Flashing talons clamp into rivals while antlers and fangs rip each other apart. Many fights between two of these monsters end in the death of at least one participant- a much higher rate than a natural animal population could sustain.
Although these monsters are incompatible with human life, certain people are able to make use of them as mounts. People touched by dark powers or with strong and deep connections to nature may be able to summon a peryton to their aid. Mistreatment of this bond always ends with a torn heart and a peryton with a newly claimed territory.