"A thousand years ago, the Crystal cracked, and here, far from the castle, the race of Mystics came to live in a dream of peace. Their ways were the gentle ways of natural wizards. Yet now there are only ten. A dying race, numbly rehearsing the ancient ways in a blur of forgetfulness. But today, the ritual gives no comfort. Today, the wisest of the Mystics lies dying. Today, they summon the one who must save them."
At the last Great Conjunction, the urSkeks were divided into two races -- Mystics and Skeksis. The four-armed Mystics (also called urRu) took on the sorrows of the world. They inherited the mystical wisdom of the urSkeks, but were powerless to use it outside their own valley. Their hopes for redemption rested on Jen. There were originally eighteen Mystics, but by the time of the Great Conjunction when they rejoined the Skeksis, only eight remained.
Despite the separation, there was still a spiritual link between each Skeksis and Mystic counterpart, a constant reminder that they were only halves of the same being. If either was wounded, the other felt the pain and suffered an identical injury. If one died, both died.