First, I will pimp out Mongoose Publishing's Slayer's Guide to Duergar.
To me Drow are much more nasty, but they are sadistic on a whole other level. Duergar, I would think, are much more practical, like the above post. Almost like Kobolds, with just more of a Punch.
Magical Missiles (Maxed for the most punch) right to the familiar. Poisons that cripple and blind (They're immune to certain poisons, so they could just smear it on their hands and use like so). Thunderstones and Tanglefoot bags every man would be outfitted with. Grease (on weapons).
They are immune to paralysis, so maybe there's a Duergar cleric with some pet Ghouls. When the alarm goes off, they set loose the starving ghouls to go 'hunt'.
Here's some ambush tactics: have the party go down an area, and find a wounded thing. Animal, person, whatever. It's crying for help, or near death. They go over, and *WHAM*. Invisible duergers. Or a pit trap that not only hangs the wounded individual, but drops the PC. Or a little illusion that the wounded individual is actually a poisonous creature.
Or a lone Duergar, who surrenders. When they get up close, *BAM*, invisible weapon (Make him a rogue, by the way, for sneak attack damage), and then have the ambush begin.
With their large dark vision, have some Heavy (Or even Giant crossbows) set up. PCs charge the bowman, and then some Duergar are hiding behind stalagmites, waiting for the PC to run past (Likely with a trip wire, or other nasty trick, or just flanking sneak attacks). Or maybe just charge the spell casters once the Fighters are allready running into the darkness.
In a book I read, dwarves had constructed catapults which fire around corners of tunnels.
These guys would definetly be bullies, and the more there are, the more superior they are.
Oh. And, whatever they can do th distinguish a party's light source. Torches? Pyrotechnics, buckets of water, Gusts of Wind, Control Flame. Magical lights? Everburning torch? Dispel. Since they have massive Darkvision (And this surpasses PCs vision with magical light), they will definetly be hitting form distances.
