Wesen

Wesen (pronunciation: VAY-zin, Grimm: VES-sin; Germ. "a being", here "creature"; Spanish: espiritu bestia "spirit beast") is a collective term used to describe the creatures visible to the Grimms. They are the basis not only of the fairy tales that the Brothers Grimm have compiled, but also of the many legends and folklore from many cultures (i.e. Blutbad, Dämonfeuer and Wendigo).

Characteristics
To date, if there has been a study on Wesen origins, it has not surfaced. Even Sean Renard, who is a half-Zauberbiest of royal patronage, has not heard of any such study and the only studying he's aware of, done by Grimms, has been how to kill them. Wesen are liminal, that is, they display two states of existence simultaneous within one physical body. Physiologically, Wesen are parahuman, exhibiting two distinct sets of DNA within the same system. Albert Denswoz and his followers refer to themselves as Duo homo instead of Homo sapiens. Because some Wesen tend to de-humanize themselves in this manner, many treat humans as we would treat animals.

When in human form, Wesen are, by all accounts, physiologically that way and thus can pass as human. However, certain aspects about them still sets them apart from the rest of humanity, such as the addictive effects that Jay has upon them (which would otherwise be fatal for humans) and their susceptibility to the Yellow Plague. Every creature encountered by Nick Burkhardt are Wesen (excluding La Llorona and Volcanalis).

The community consists of both good and bad creatures ranging from Blutbaden to Bauerschwein to Mauvais Dentes. Individually, Wesen generally behave stereotypically in accordance to their own kind (i.e. the Blutbaden being fierce and vindictive, Siegbarste being dangerously vengeful, or Mellifers for their hive-like mentality and penchant for sending messages). Some Wesen follow ritualistic practices passed down through history (i.e. the Aseveracion and the Roh-hatz). Other than the Grimms, keeping the Wesen in check, only the Seven Houses are aware of the real workings of the world, the majority of humanity is blissfully unaware of their existence.

Ziegevolk, Musai, and Cracher-Mortel all have abilities that allow them to influence or have complete control over people. Ziegevolk use their pheromones to control and manipulate whoever they want, usually women. Musai's lips secrete a psychotropic substance, making its kiss known to be very euphoric and addictive. After they kiss someone, they are able to easily manipulate their victims, who will do whatever they have to, to prove their love for the Musai, even kill someone or die themselves. Cracher-Mortel have the ability to create an army of zombie-like victims by spitting tetradotoxin on to the face of a victim, which seeps into the skin of the victim and shuts down the neurosignals of nerves and heart cells, and causes suspended animation. Atropine and scopolamine toxins reanimate the victim in a zombified state. In this state, the victim is in a trance and will perform whatever task is asked of them by the Cracher-Mortel.

Despite being parahuman themselves, many Wesen eat humans (ex: Blutbaden, Schakals, Wendigo, Coyotl, and Mauvais Dentes) or other Wesen (ex: Blutbaden eat Bauerschwein and Seelengut, while Lausenschlange eat Mauzhertz).

Some Wesen, like Raub-Kondors hunt other Wesen, such as Glühenvolk, for their skins. They use a potion called Sauver Sa Peau to keep them woged after death for up to 8 hours so they can skin them.

In Nick fights with Adalind and gets her to bite his lip causing him to bleed and some of the blood gets into her mouth. A few seconds later, the Hexenbiest spirit inside of Adalind leaves her body causing her to become a normal person, and lose all of her powers. So far this is the only time that a Wesen became a human. It's unknown if Grimm blood affects other Wesen types the same way.

It may also be possible to turn Wesen into normal humans via drugs. Konstantin Brinkerhoff pioneered a series of medicines that would supposedly remove the ability to woge. While the experiments were undoubtedly a failure, it must be pointed out that Brinkerhoff insisted that the drugs would work if he'd been given the time to perfect the dosage and delivery system. It was also unclear as to whether the drugs interfered with other Wesen abilities such as enhanced smell (Blutbaden) and increased bone density (Siegbarste).

Genetics
The complexity of Wesen genetics yields some interesting questions. Monroe and Rosalee have some answers: In a grundfalsch (fundamentally flawed) mixed-Wesen relationship, there is a Vorherrsch (prevalence)-- the offspring will be the "more dominant" Wesen type. There are health risks for the developing offspring, of course.