There is a ritual that allows a mage to steal the soul of another person. This adds their mana to your own, making your magic more powerful. It also extends your lifespan and makes your physical form stronger and more durable. Absorbing mana from numerous victims in this way can make you almost godlike. The downside is that it mutates your form in various ways. Mages will eventually exhibit deformities such as extra limbs, elongated fingers, pot marked or bark - like skin, and other mutations. A dark aura emanates from them that a glamour spell cannot hide. These mages are called crones. This Coven seeks to overthrow the establishment of the mageocracy and take power, and are biding their time for the right moment.
This kind of magic is considered a form of cannibalism, for you are absorbing an individual's soul into yourself. Not only are you stealing his life energy, you are preventing the soul from passing on to the next life. Crones are the scum of this mageocracy and are feared and hated by all. Many have gone on to be powerful threats as the Hitler of this setting.
This coven needs to hide their presence from authorities, or they would be hunted down and killed. Being chased to the fringes of society to hide out in the woods is not conducive to their plans and defeats the purpose of gaining power in the 1st place. They also need to gather more victims to sacrifice in order to add to their strength. How can they operate in society without being discovered?