Shadow King

Tomb of the Shadow King
You meet him at the entrance of this quest. When you talk to him, he will reply:
 * Shadow King: Glad to see you've finally made it. Time is short, Nerezza is finishing completion of the Twisted Apocrypha, there's no time for dilly-dallying.
 * You: Ok. So we'll be going then.
 * Shadow King: Wait wait. Things you should know. Nsu is the guardian who resides here. He is most accustomed to the darkness and abhors the light. To wake him, all the lights must be darkened. He draws power from the darkness, so you'll need to lure him to the chamber at the end of the tomb. There you can trap him and activate an intense light. This will drop his defenses and render him killable.
 * You: Nothing is ever easy or straightforward with you shadow guys is it? So first all lights go out, then one light goes on, got it.
 * Shadow King: Nsu has two guardians, Keepers of the Light. They must be destroyed as well.