The PCs are higher level than they "should" be (6th level now, just cleared the Chamber of Eyes!) but I don't care. Tonight I think they are going to hit the Horned Hold - after they deal with the Mages of Saruun in the Seven Pillared Hall trying to arrest them for wiping out House Azaer.
Frankly, the Duergar are way tougher than their levels would indicate, so Level 6 sounds about right. They are nasty, nasty little guys with high defenses and dirty tricks.
(0) All duergar have those nasty beard quills. Minor action, decent damage, ongoing poison damage,
and a lingering effect. Ewww...
(1) The Duergar Scouts will, generally, be able to use their Sneak Attack every other round or more. Their invisibility refreshes on, IIRC,




They are damage machines.
(2) The Duergar Soldiers (Guards, maybe?) have really high defenses, hit a lot, and hit hard. Their ability to ignite is just icing on the cake.
(3) Theurges are
insane... Their area attacks are huge; their allies are mostly immune to them; and the PCs will spend probably half the encounter blind, prone, or both.
(4) Shock Troopers are really the only somewhat overrated Duergar, although they hit insanely hard after growing to Large size.
Exercise caution. Also, a lot of the Duergar will retreat back with their buddies when they're losing. This makes future fights very, very difficult.... My group had to barricade themselves into a cleared Tower to get a quick night's rest, and escaped through a chimney when the Duergar started trying to smoke them out.
-O