Shapeshifters

In many cultures there are tales of shapeshifters. These normally fall under three broad groups; Fey creatures, religious fanatics & cult members, and general others. Each uses a different method to transform, and many have specific forms they regularly transform into. Magic is regularly involved in some capacity, and a good few have an innate ability too, whether through the type of creature or where they come from.
It is common for many Fey to be able to shapeshift, and in most countries that have these types of creatures, many are seen as tricksters. Certainly in Europe, the Fey have a strong bond with the land and the people who believe in them. A few others are found further afield with places like China having stories of shapechanging trickster foxes. Nearly all Fey are innately magical, having this ability to shapeshift inherent to them. A few don't, and a few have the ability to turn invisible instead. A rare few have both abilities. Depending on the species, it affects whether they use it to help, harm, or in a trickster capacity. Some, like the Selkie, who are usually neutral, use it for the sole purpose to travel on land when they feel like it. Others like the Kelpie to capture prey, drowning their victims before eating them underwater. Very few are actively good natured enough to use it to benefit others. Some, like the Pixies will use it to scare off anything that would threaten the forests they live in, and maybe guide innocent creatures out of danger. Some of the worst, like the notorious types of Hags, actively use it regularly for out-and-out harm, just because they can. For some reason, the Fey have a fear of iron & magic, and it seems this combination may have some effect of preventing the shapeshifting.
Religious fanatics & cult members sometimes have shapeshifting abilities. Groups like the Scandinavian berserkers, and some of the witches & witchdoctors in Africa, will use the pelts / skins, or pieces of it (such as a belt made of a part of a pelt), to turn into an animal. The former can be split into three groups using the pelts of bears (the most common), wolves (the second most common), or rarely, boars. They are usually family orientated cults, with the men especially involved. They worship the animals for their strength & ferocity, and regularly wear little armour in combat. By force of will they transform into a hybridised form, protected from iron weapons, and fire, slaughtering anything that moves. When battle or religious ceremonies end, they revert back to their normal form.
The latter generally uses the pelts of animals, like the lion, the jackal, or the hyena. The witchdoctors and the like that use the lion form are or similar, are generally more prone to act for their communities. They see themselves as protectors and the like, and see the lion as being strong & proud, taking on the animal's strength. The latter are generally more feared, seen as scavengers, and evil tricksters who revel in misdirection, and attacking those more vulnerable than themselves. The witch or witchdoctor uses these to terrorise others and whole communities.
The remaining creatures that shapeshift are specific species or diseases. Vampires, lycanthropes, and dragons are the most common. Creatures such as the Doppelganger are another bunch. Vampires and Lycanthropes are diseased or cursed individuals that are either undead, or suffering the curse of the Lycanthropy disease. These have a fear of silver, and can be injured by that metal. They can change into creatures like bats or mist if vampires, or specific animal forms in the case of Lycanthropes. The former is forced into the mist form if they are seriously injured and need to return to their resting place to heal. They can pass this on to others during feeding on their victims blood, and the victim does the same to the vampire. Lycanthropes are either born naturally with the disease, afflicted by it if bitten by one or cursed with it. Many of them are forced to change into hybrid forms or animal forms under certain conditions. Both of these are found in some form or fashion throughout the world as a whole. Many of the forms have been attributed to specific regions depending on the strain of vampirism, or the animal of which the lycanthropy was originally tied to (or found in the region if caused by a curse.
Dragons in many cultures can shapeshift into a human or humanoid shape. Not all do, but the ability is there. A few types prefer it to others, such as gold dragons, where they can interact with humans & other creatures more readily. This cannot be passed on, but any children conceived while in this form have aspects of the dragon's type.
Doppelgangers are a race of beings that are found mainly in Europe. They have the capacity to naturally shapeshift. Exactly why is not known, though it is speculated that they have a mix of Fey & Aberrant blood in them. This could explain why. They try to imitate others around them, slowly killing their victim, while extracting their mannerisms & memories for use in their victim's guise.
Jackalweres and wolfweres are another rarely encountered creatures. The former is African in origin, and the latter is European. They are both animals that are found regularly in a bipedal form of animal, and can manipulate human & humanoid objects. Both are able to shapeshift into animal form at will, and appear slightly larger than their natural counterparts. They regularly lead a mix of their own kind and packs of their cousins. Only by breeding with their own can they breed true. It is not always successful when with their cousins. No-one knows exactly how these shapeshifters came about, yet there is a couple of ideas as to how. The first is that a pack of each animal was cursed at some point in time, leading to the appearance of the first jackelweres & wolfweres. The second is that in both instances they killed & fed on a human or humanoid with some form of lycanthropy that mutated & spread to them.