Martinthewarrior post is completely wrong. Omegavegeta is right.
It's a lottery spawn through Bonecutters in the little rooms where he spawn.
the other Nms of that floor have nothing to do with it.
I have experienced a 30min-2hour1/2 spawn time by killing the placeholders almost as soon as they popped.
I'm a ranger 64 and I got charmed once out of 6 tries of Enky, so I think anybody can get charmed. Because of that charm ability I suggest people to camp him alone, or kill their friends >.<.
One of my friend pld's killed my friend drg because of that...
Anyway, I'm 0/7 and bored. Thought 7 was the lucky number but it doesnt seem like it ; ;
Sooooooooo, happy hunting, but not when I'm there :P