Tengus are bird-like nature spirits (yokai, or kami) from Japanese folklore. Their name means sky sentinel or sky dog, which is a remniscient of the very first tengu from the year of 720, who had more canine features.
Although consensus how a Tengu looks like is varied, some form of avian features are usually present. Typically Tengu has human torso, wings, and a bird's head with vague resemblance of a human being. Sometimes they are depicted in almost fully avian form, but able to manipulate objects such as weapons, or almost fully human form with unnaturally long nose, or a combination from all of these.
Tengus are able to fly, and depending on their type they may know how to use magic. Folkloristic Tengus might be able to do some petty magic, while demonic Tengus can possess people. All the greater Tengus are formidable fighters, as their avian and supernatural origins give them superior coordination capabilities.
Types of Tengu
Tengus are neither good nor evil. In fact, there are multiple types of Tengu, all of which have their roots in spiritual origin. Since then they have diverted towards many different paths.
Tengus can be nature spirits that have their own agendas. Often these Tengus have mercurial disposition, and such unpredictability may have them seem like more oriented towards evil. But since they are not particularly bright, humans may be able to outsmart them and even gain valuable magical treasures.
There are also evil Tengus that have serious resentment towards religion and especially Buddhism, and on many accounts tease and torment monks and priests. They can also take the form of a priest to mislead others. These kind of Tengus are more demonic in nature, and are even able to possess people. Sometimes a heretical priest who has died has become a Tengu, and depending on their level of enlightenment they would become more or less powerful variations of Tengu demons.
Also, good and beneficial Tengus exist that were worshiped as mountain and forest gods. This type are even approving of religion and protect Buddhist monks in remote locations. Now and then a good Tengu might fall victim to excessive pride or other negative personality trait and become an evil Tengu. Good Tengus still weren't all that compassionate and kind-hearted, and would fiercely protect their sacred lands from intruders.