Lycanthropy in the Leakyverse is the result of a Dark Magic curse, transmitted from lycanthrope to human through a bite - non-humans such as goblins, giants, and other humanoids are immune to lycanthropy. The main manifestation of the curse takes place from rise to set of the full moon every month, at which point in time the person under the effects of the curse transforms into a specific animal, determined by the nature of the lycanthrope who administered the bite which cursed them. There are lycanthropes of most of the major predator species, wolves, tigers, and lions being the primary types although others have been known as well. The animal which the afflicted person transforms into is not a "normal" animal of that type, but one that is particularly vicious and bloodthirsty in the desire to attack humans.
When in animal form, only other animals and animagi are safe from the bite of a lycanthrope. Any other human is at risk for being attacked and either killed or infected, even humans that the lycanthrope might recognize as "pack" when in human form. The only exception to this rule are generally the human children of the lycanthrope, and if the species of lycanthrope in question is capable of taking a mate, then that mate if they are human.
At all other times, the human who is infected with lycanthropy is indistinguishable from any other human. There are, however, certain physical traits that a lycanthrope gains when in human form as a byproduct of the curse. Lycanthropes tend to be faster, stronger, and physically tougher than a normal human, and even tougher than wizards. Accelerated healing is also a common attribute, except when the wounds or damage is inflicted via a vector containing silver, since silver is a systemic poison to lycanthropes. In addition to these general traits, lycanthropes have other physical advantages related to the animal form of their curse - werewolves have exceptional senses of smell and hearing, while others have exceptional eyesight or other enhanced abilities.
Conservation of mass tends to hold true, and so lycanthropes in their animal form usually weigh close to what they weigh in human form. For werewolves, this means that the wolf in question is usually rather large, while for tigers they tend to be somewhat smaller unless the human puts on weight after infection.
Mentally, lycanthropy lends a rather unique duality of nature to the afflicted human. During the full moon, the characteristic animal completely takes over, not just the body via the physical transformation, but the mentality of the human is totally overpowered by the animal. For the rest of the month, the human can "feel" their animal below the surface, almost like a second personality with a distinct set of desires and emotions and goals of its own. The animal nature can even come to the fore during times of intense anger or stress, which has lead to a great deal of misunderstanding and fear. Lycanthropes can learn to control the Dark side of their natures, through various mental techniques including meditation. It takes a great deal of discipline to develop the mental control, and some lycanthropes can never master their beasts, which can lead to mental degeneration or even insanity. It is important that newly made lycanthropes be counseled and educated as soon as possible, so that they can learn the mental control necessary to allow them to function normally in human society.
Werewolf specific information:
Werewolves are the most common of all lycanthropes to be found in Europe and North America. Werewolves have actually managed to develop something of a "culture" unique to themselves, due to the fact that in most countries werewolves are looked upon with fear and hatred, and in some cases are automatically classes as criminals merely for existing. This has lead to some instances of the outcasts banding together into packs, each of which tends to follow a wolf-pack type of hierarchy. This means that there is an Alpha, and a descending set of levels under that which other werewolves occupy. The Alpha is the leader of the pack, responsible for making most decisions regarding pack structure, occupation, and politics. Succession is not based on heredity - since werewolves are made, not born - and any werewolf who can subdue the current Alpha in physical combat becomes the new pack Alpha.
Not all werewolves are members of formal werewolf packs. Many tend to avoid the company of other werewolves in order to not draw attention to their condition or to raise suspicion or incite retribution of other humans. However, it is not uncommon for werewolves who are on their own to develop something very like a pack among their closest human friends.
Another peculiarity of werewolves is their habit of taking a "mate". Other species of lycanthropes have different family structures depending on the habits of their specific animal - weretigers, for instance, do not tend to form family units and remain more solitary - but werewolves can, if they so chose, mate themselves to either another werewolf or a human partner. The mate is not chosen by the human side of the lycanthrope, but by the wolf. Almost always the human side is physically attracted to the potential mate, as well, but the actual bond is formed between the lupine nature of the lycanthrope and the mate in question. And while a human who is afflicted with lycanthropy may have many lovers, or even spouses, during their lifetime, the werewolf only ever chooses a single mate. Once bonded, if the mate dies, the lycanthrope will generally pine until they die as well.
Male werewolves can father children, and female werewolves can bear children, although this usually rare. The children of a werewolf are always human, and inherit no special traits from their werewolf parent.