What is a "Jachyra" in the novel, The Wishsong of Shannara?

A Jachyra is a dangerous creature formed from dark magic. It is red and muscled, with hooked claws and gleaming yellow eyes. It is a creature from another age, locked away long ago with fairie magic, brought back to life again to protect the dark magic of the Ildatch. The Jachyra becomes the ultimate adversary for two important characters in the novel.