There are a wide variety of shapeshifters and they are as follows (Note the description will describe wolves because of popular folklore, but there are many animals that one could transform into and the rules are the same). There are also rumors of animals who can turn into humans, a reverse werewolf so to speak:
“classic” Werewolves (or Werecreatures)
The “classic” werewolf is someone who uses magic to transform themselves into a wolf. This is not necessarily a wizard or well-trained practitioner of magic, since the transformation spell will work for anyone who learns it. The physical body is transformed, but the mind remains the same. This can be a disadvantage in the beginning because, although the person gains all the senses of a wolf, they do not have the life experience of using them. The werewolf must learn to use smell and hearing as their primary sensory input rather than sight, and learn to move and react to their environment as a four-legged creature. All this takes time, but the werewolf can eventually learn to do well in their new form. The wolf form has all the natural capabilities of an ordinary wolf; silver is not needed to kill them and they do not heal wounds any more quickly than normal wolves. This type of werewolf can reassume its human form whenever it wishes.
The transformation spell can be cast on another, forcing someone to assume the form of a wolf (or any animal the caster chooses). This is a violation of the Second Law of Magic, because the mind of the transformed person is eventually lost and all that is left is the mind of a wolf. If the spell is reversed in time, the victim will recover; however, once lost, the personality cannot be restored and the person is, in a sense, dead.
A hexenwolf uses a talisman imbued with powerful magic to transform itself into a huge wolf. The hexenwolf’s wolf form is much larger and more powerful than any natural wolf, possessing enhanced speed, strength, and ferocity. The only part of the hexenwolf that is unaffected by the transformation are the eyes, which remain the same color as their human form. The talisman itself may take many forms, including a ring or amulet, but most commonly appears as a belt made from a wolf pelt. The talisman engenders the transformation by providing an anchor for a spirit of bestial rage, and is activated with an incantation by the wearer. This spirit protects the human personality while in wolf form. However, the hexenwolf loses all human inhibitions and runs more on primal human desires. The hexenwolf can be wounded or killed by normal weapons and can be forced to transform back into human form if someone manages to remove their talisman. A hexenwolf may reassume human form at will, but the power that the talisman gives the user is addictive—in many cases, this addiction begins to affect the user’s mind and personality in human form, much like a drug addict needing a fix. The most seriously afflicted lose all impulse control, becoming violent and sociopathic.
A lycanthrope is someone who is a natural channel or medium for a spirit of rage. The lycanthrope is born with this ability; it does not allow them to physically change into a wolf, but grants them a beast-like strength. When this spirit takes over, the lycanthrope becomes stronger, more aggressive, and more resistant to pain, injury and sickness. They heal wounds rapidly and tend to congregate in groups much like packs with an Alpha leader. Although harder to hurt or kill than an ordinary person, lycanthropes can be killed with ordinary weapons.
A Loup-garou is the closest to the monsters of legend. These werewolves have been intentionally cursed by someone, usually a very powerful sorcerer, demon lord, saint, or one of the Faerie Queens to be possessed by a wolflike demonic entity at every full moon. They become near-mindless killing machines with supernatural speed, strength and ferocity. They recover from injury almost instantly, are immune to poisons as well as any kind of sorcery that attacks the mind. They can only be killed by a weapon made from silver which has been inherited—not just purchased. The curse of the loup-garou can be hereditary if the one who placed the curse specified it as such. Usually the person afflicted with the curse is aware of their condition and will have enough sense to isolate or shield themselves from society to prevent the horrible damage they would inflict on the rest of the people with the next full moon.
The skinwalker, also called the naagloshii, has the ability to change itself into an enhanced version of any animal and can use magic extensively. Its true form is that of a golden-furred semi-humanoid. Naagloshii gain power by hunting magical practitioners and devouring their power; most are millennia old and thus have acquired extreme power, to the extent that even powerful wizards avoid fighting them if possible. They are, however, not invulnerable – the WardenDonald Morgan relates an encounter with a naagloshii he had in the 1950s, which he ultimately defeated by luring it onto a government nuclear bomb testing site in Nevada, then escaping into the Nevernever seconds before the bomb detonated, killing the skinwalker.