There are many types of werewolves, but the most common type is created when a human makes a pact with a demon in order to become one. Any sort of demon can manage it, so long as the would-be werewolf knows the right ritual.
Even an imprisoned demon, like one of the Five, can make a pact if the petitioner is close enough to the place of imprisonment, which does away with the need to summon a demon first. The ritual creates an ointment which is spread all over the naked flesh of the one who desires the power of the wolf.
Such werewolves have preternatural healing, strength, and speed in either human or wolf form, though more so in the latter. They can switch between forms, as well as take on blended forms, at will. They can command wolves to do their bidding.
If not killed using silver or a holy object, the pact werewolf’s corrupted soul “jumps” to another wolf somewhere nearby, which transforms back into the werewolf’s human body in daylight.
If killed with the right instruments, the werewolf reverts to her human shape, whereupon all the wounds she inflicted on others as a monster are inflicted on her in turn, alive and screaming. There is usually nothing left afterward.
Pact werewolves cannot maintain their wolf form in sunlight, and take unusual amounts of damage from the silver or holy weapons needed to destroy them. In human form, if a pact werewolf is cut, the wound sprouts fur before healing.
Pact werewolves develop a taste for human flesh. Over time, it becomes more delicious to them, occulting all other pleasures. The flesh of those related to them, by blood or association, is particularly delicious.