A Thestral is a breed of winged horses with a skeletal body, face with reptilian features, and wide, leathery wings that resemble a bat's.
They are very rare, and are considered dangerous by the Ministry of Magic. Thestrals are, undeservedly, known as omens of misfortune and aggression by many wizards because they are visible only to those who have witnessed death (and fully accepted the concept) or due to their somewhat grim, gaunt and ghostly appearance.
Thestrals can be domesticated and mounted, so they are used as an alternative to brooms, Apparition and other methods of transportation. Once trained, they are very diligent and will quickly carry their owners wherever they wish to go.
Due to their classification as XXXX, only experienced wizards should try to handle Thestrals. Breeding as well as owning these beasts may be discouraged or even illegal without Ministry consent; in fact, wizards that live in areas not protected against Muggles are forced by law to perform Disillusionment Charms on their Thestrals regularly.
Thestrals have quite a disturbing appearance and the wizards who are capable of seeing them often only describe these creatures as being sinister and spooky. This is because they are seen as having big, bony figures and their dragon-like faces which bear white, glittering eyes that lack both expression and pupils.
Being a type of winged horse, most of their anatomy is identical to a horse, excluding their large wings that sprout from their back. Unlike the Abraxan , another breed of winged horses, Thestral's wings do not possess any feathers at all; they have vast, black and leathery wings that are more similar to those of bats.
Their fleshless, lustrous bodies are covered with a translucent and glossy coat. This smooth and dark skin is a bit slippery and so thin that Thestral's bones are clearly defined through the entire extension of their sleek bodies.
These eerie horses have long black manes, as well as a large tail, either with flowing black hair, like horses or ending in a tuft, like zebras. Another distinction is their sharp fangs used to seize and slash their prey.
These creatures are seemingly rather dull, though Professor Rubeus Hagrid states that they are "dead clever", and, in fact, trained Thestrals are smart enough to understand their rider's words when they ask to travel to a specific location.
These magical creatures can be found in dark environments, and the forest is their natural habitat. They communicate with each other through a shrill and strange yell that resembles some sort of monstrous bird.
They appear to be loyal creatures, able to discern a friend from an enemy. Thestrals would forcefully attack anyone or anything they see as a threat and, in the unusual case of domesticated Thestrals, any enemy of its owners.
In the Battle of Hogwarts, Hogwarts' trained flock of Thestrals cooperated with Buckbeak, the Hippogriff , to attack the Giants fighting for Voldemort. It's unclear whether or not wild herds can similarly cooperate with other species.
Thestrals are carnivorous animals and are attracted to the smell of blood. Professor Wilhelmina Grubbly-Plank mentions that they often attack birds. This indicates that, naturally, they hunt not only for food in the ground, but also pursue flying prey.
The Thestrals that live within the Hogwarts grounds, in the Forbidden Forest, are properly fed and well trained. They don't attack other creatures or students unless seriously disturbed.
The Thestral tail hair is a powerful and tricky substance that can be mastered only by a witch or wizard capable of facing death. It should be noted that this substance can be used as a core in a wand's conception and it was used to create the most powerful wand known by wizards, the Elder Wand.
The most well known ability of these beasts is their invisibility to those who haven’t seen death. In other words, they are only visible to people who have seen someone dying and fully accepted, understood and internalized the concept.
Thestrals have an extraordinary sense of smell and will easily recognize the smell of blood and fresh flesh, even if the source of the scent is rather distanced.
They also have quite a useful sense of direction. The Thestral can understand exactly where their riders need to go. If their riders have a certain destination in mind, they only need to say the destination and the creature will diligently carry them to the intended location - much like owls do with letters.
These gentle, winged beasts are very capable and fast fliers and can travel long distances hardly beating their large wings. For example, in 1996, six members of the Hogwarts herd were capable of flying from somewhere in Scotland to London in a brief amount of time.
Their powerful wings are capable of lifting, at least, the burden of two humans plus their own weight.
Even with all their useful abilities, Thestrals are rarely used as methods of transportation due to their reputation as omens of evil and their somewhat dreadful and even distasteful appearance.
When riding a Thestral, the traveller usually holds the creature's mane to ensure balance during the flight (or ride.) To aid the mounting, the wizards also place their legs behind the wing joints to provide safety.
Flying on the back of a Thestral during a long journey is frequently an unpleasant experience, particularly to those who dare riding them without seeing the creature. The high speed flight on an invisible steed can be terrifying. The wind will, eventually, cause a temporary deafness and will force the riders to close their eyes. It is often difficult to keep balance on their slick backs.
The Hogwarts herd is gentle towards humans , they react satisfactorily to caresses and avoid attacking owls. However, taking into consideration the Ministry of Magic classification as "dangerous", this behaviour may be exclusive to well-trained Thestrals, or just mere prejudice from the Ministry