Werewolf

Werewolves are a race of partially-human supernatural creatures, able to morph into a combination of human and wolf, that have been encountered by hunters such as Sam and Dean Winchester. It has been stated that werewolves and skinwalkers are cousins. There is no known cure for lycanthropy.

Characteristics
Werewolves are humanoid carnivores, the ultimate combination of wolves and humans. They feed on prey found nearby, which, due to the increase of urban areas, are mostly humans. When they devour the flesh of victim they leave a recognizable trace on the prey: they always eat the heart, and although they do sometimes eat more of the body, but never leave the heart. The transformation only occurs after a werewolf bites a victim, the way werewolves continue the spread of lycanthropy.

In their werewolf form, their bodies change rapidly, changing into a fitting definition of predators. Their nails increase to sharp, long claws, fangs increase in size and eyes resemble those of a wolf rather than of a human.

Types of Werewolves
There are two types of werewolves shown in the series: regular werewolves, and pureblood werewolves.

Regular Werewolves
Regular werewolves can only turn into a werewolf during nights coinciding with the peak of the lunar cycle during their sleep - as Sam and Dean checked if they succeeded in stopping Madison from turning into a werewolf again by remaining in her apartment during a night under a full moon, and no werewolf transformation was seen while she was awake. However, when the next night arrived, Madison turned during her sleep and went on another feral rampage.

In the series, the people affected by the disease have a short-term memory loss, often leaving them in confusion of wounds which might have been caused during the night. In the series, Dean manages to cut Madison with a silver knife, making her wonder how the wound was created.

Despite having no control over and during their transformation, certain fragments of their personality and fears can be imbibed by the werewolf's mind, especially strong ones. Aside from hunger, suppressed fears or aggression can drive them to kill in their beast form. As such, a werewolf's attack may be controlled by these emotions, depending on which one is dominant. When Madison was attacked, she was turned into a werewolf when her attacker felt an intense drive to mate. On another hand, Madison defensively killed a stalker when she felt that the man was becoming too invasive with respect to her privacy.

Pureblood Werewolves
Werewolves that are closer to the Alpha up to the fourth generation are referred to as Purebloods. They have more control over themselves and are less feral. Their human side retains a lot of control and they remember what happened after their transformation. They can transform anytime they want. Purebloods can also access some of their werewolf powers such as enhanced strength and speed even while in human form.

Purebloods can also feed on just animal hearts, but if they get a taste of human hearts, it is harder to control themselves. They will be drawn to eating human hearts, the temptation escalating with each heart eaten. It is still difficult for them to eat animal hearts even if they can resist (one stated he had to force himself to swallow them). Its indicated that purebloods are both those bitten by a first, second and third generation werewolf and those who are offspring as it has been shown werewolves can have children and one werewolf existed that was fourth generation.

Powers and Abilities

 * Shapeshifting - Werewolves transform into a wolf-like creature only under a full moon. However, Sam tells Dean that werewolves no longer change under a full moon, but under half moons. The demon Crowley agreed with Sam by saying "werewolves changing under a full moon, so... 09". It is presumably because of the upcoming arrival of Eve. Following her death it appears to have shifted back as Sam and Dean were later surprised to be dealing with Werewolves outside the full moon. Pureblood werewolves can shape shift at will and transform anytime they want however, they somewhat lose control whenever they feed on human hearts.
 * Infectious bite - Through a bite, a werewolf can turn another person into a werewolf while in beast form.
 * Claws and Fangs - Werewolves have powerful claws and are able to cut solid walls. Their fangs can tear off and eat human flesh and can rip out a human heart right out of their chest cavity.
 * Supernatural Strength - A werewolf's strength is much greater than a human's. They can easily overpower humans and can rip flesh and bones with amazing force, their strength is notable even for monsters, able to smash stone with there bare hands. All werewolves seem to have the same or at least a similar level of strength.
 * Enhanced Agility - Their agility is greater than humans, often allowing them to perform incredible jumps and sprints easily.
 * Super speed - A werewolf can move very fast; they are able to move from place to place in seconds.
 * Super stamina - Werewolves don't tire easily.
 * Super Senses - All werewolves are able to see better than humans in darkness, similar to actual wolves, their sense of smell and hearing is equally enhanced.
 * Invulnerability - Werewolves can't be killed by conventional means and weapons. Silver however, can kill them.
 * Regeneration - Werewolves can regenerate all non-lethal damage, purebloods are even able to completely heal their orginal bites.

Vulnerabilities

 * Silver - A werewolf's only known weakness is their vulnerability to silver, as they can be killed with a silver knife or bullet. Contact with silver will hurt them.
 * The Colt - As the colt has the ability to kill almost anything, it is most likely a weakness to werewolves.
 * Vamptonite - Edgar states the Leviathan additive will kill werewolves as well as vampires.
 * Severe Dismemberment - Signifcant damage can kill them, Kate is able to kill Brian Wilcox by ripping him to shreds.

Known Werewolves
There have been seven werewolves that have been on the series:
 * Alpha Werewolf
 * Madison (deceased)
 * Glen (deceased)
 * Professor Ludensky (deceased)
 * Michael Wheeler (deceased)
 * Brian Wilcox (deceased)
 * Kate
 * Garth Fitzgerald IV
 * Bess Fitzgerald
 * Joy Myers (deceased)
 * Reverend Jim Myers
 * Sheriff Pat (deceased)
 * Russ (deceased)
 * Jobah (deceased)

Trivia

 * Have been mentioned more often than any other monster (13 times), but have only appeared three times.