An Explanation of Wesen.

Wesen (Pronounced "Veh-sin" or "Veh-sun") is a term used to describe the creatures visible to the Grimms and sometimes to normal humans. 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.

Abilities of Wesen:

Wesen come in many different species, abilities depending on that species. Some have immense strength, others have bodily weapons such as stings in true form. The body parts of many Wesen (e.g: their hair) can be used to create intricate spells and potions. However, bear in mind, the powers, characteristics and appearance of a Wesen always depends on the species. Wesen is a collective term for the creatures, and each species has it's own name and, as said above, special abilities. 

There are also some Wesen hybrids, for example a Wesen and Human hybrid, or two different spices of Wesen forming a child. The abilities of these are never clear, however.

The History of Wesen:

Wesen are descended from an ancient set of Wesen races known as Pureblood Wesen. Purebloods exhibit traits which make them seem immortal and God-like compared to humans, and in ancient times, many of them were worshiped as Gods and Goddesses. Today, however, Purebloods tend to try not to attract attention in an arguably more dangerous world and instead pull ropes on a quieter level than they once did. In doing so, they have generally lost their religious significance, becoming legends to Wesen and myths to Kehrseiten (Kehrseite is the name Wesen use for normal humans, pronounced "KERR-zy-tuh". Kehrseiten is the plural of Kehrseite).

During and before the fourth crusade, Wesen were used to fight in the armies of the Royal Families, who used the Grimms to control and police their Wesen armies. Over the years, the Royal families either lost so much global power and influence that they could no longer use the Wesen as armies, or they had no need for Wesen soldiers and let the creatures spread across the world. (An in-depth description of the Royal families shall feature in the next chapter, so do not worry if you don't understand this information).

There are a few Wesen that are featured in The Hidden Girl, but I will not mention them because of spoilers and the fact they are not so deeply involved in the plot lines. 

*This book is a Grimm guide, and it will feature an A-Z of Wesen in later chapters, giving details on every known species.