The Night Kings are the four most powerful servants of Izrador, each in their own right a superhuman being. For a sense of scale, in GURPS terms, each of them is probably at least a 500pt character, with Zardix being the most powerful of the four by all accounts.
Ardherin is the second most powerful channeler alive, second to the Witch Queen only, and she is over 9,000 years old. Ardherin and Sunulael do not like each other.
Jahzir is the most poweful warrior on Aryth, able to single-handedly dispatch with entire companies of Elves when he takes the field, and possibly stand toe-to-toe with an average Dragon. He is also the General of the armies of Shadow, currently directing the extermination of the Caransil Elves along the Burning Line.
Zardix is the Wrath of the Shadow, a colossal and ancient Dragon entirely under Izrador’s power. greatest of the living Dragons, Zardix somehow fell under Izrador’s control, and when she is sent forth, her breath is able to wither and burn everything in it’s path.