A Duergar is a colorless dwarf who is eternally not happy.  They have spent their entire existence underground wearing clothes and jewelry that reflects their bitterness towards…everything.  They are just like their mountain kin, except that they just want to control everything and enslave you just cuz you look different.  They are generally just assholes.  They just work, work, work, until they die.  They are amazing craftsmen, but they seem to not take any pride or happiness in their work, which if you ask me a shit way to live.

These Debby downers are the most annoying person to be around.  They constantly complain, are ever pessimistic, will shit on every accomplishment, will call the cops on their roommate for having a party, never pays you back, owes you rent, and never does the dishes complaining that it’s the “community dishes and we all have the opportunity to do them.”  Why are they such shits?  Probably their rich entitled parents, but lore wise, their ancestors where crazy greedy into that Jeff Bezos sort of way and dug under the underdark for riches and whatnot.  Then one day, they dug too far and met the Mind flayers.  For a long time after, they were enslaved which transformed them into the very evil that enslaved them.  Well, happy ever after, they gained their freedom and are now expressing their Manifest Destiny on the lot of us. 

What sets these sad ass dwarves apart from other dwarves, is their mental fortitude.  Because of generations of abuse, they are able to shrug off charming ladies, the illusions of hope, and other such spells that could affect them.  To add fuck you to injury, since the Duergar have been living in the Under dark for so long, they have become saturated which magic.  What can they do?  Oh just grow into the size of Ogres and become invisible.  Add some darkvision and you got an annoying as hell little guy stabbing you in the shins until you give up and get enslaved to work their mines. Fun.

Oh Cool.  More numbers.

Now I want to throw out an idea here.  In the Monster Manual, there technically is not any Duergar Commoner stat block.  I found this interesting.  Either the writers just assumed that you would just use the Dwarf Commoner stat block, or there are no “normal” Duergars.  Personally, I love the idea of Commoner Duergars always have some sort of armor and weapons on because in their very nature they are distrusting and unhappy little shits, so why not protect yourself from…everything?

The Duergar, equipped with their Scale Mail and Shield, have an AC of 16, 26 (4d8+8) HP, and a speed 25 ft. 

STR: 14 (+2):  Makes sense, all they do is fight and work.  Even their babies have 6 packs.

DEX: 11 (+0): Has the Dexterity of a normal creature. Woo.

CON: 14 (+2): Their physical and mental fortitude is out of this world.  They can’t be broken!

INT: 11 (+0): they know some things about rocks, but don’t expect them to be able to solve some linear algebra or something.

WIS: 10 (+0): perceive the world in a normal way. Woo.

CHA: 9 (-1): Should be lower.  These pessimistic party poopers exist solely to ruin your day.

Damage Resistance: Poison

Senses: Darkvision to 120 ft., Passive Perception 10

What makes them cool as shit?

Duergar Resilience:  Advantage on saving throws against poison, spells, and illusions, being charmed, and paralyzed.  Their resistance is super cool roleplay wise.  You can’t depend on magic to get by these fuckers.  If you want to make a deal with them, you can’t just use your Jedi mind powers to easy peazy your way out of situations.  It should be a saying.  You can’t trick a Duergar. Period.

Sunlight Sensitivity: While basking in the sun, they have disadvantage on attack rolls and perception checks.  Wanna kill a Duergar?  Get some sunlight.

Actions are Cool

Enlarge: For one minute, they magically increase in size including the stuff they are holding on to.  When Ogre-sized, you double their damage dice on strength based weapons, and makes strength based checks and saving throws with advantage.  Holy fuck.  That’s nothing to sneeze at that’s for sure.  Get a small army of these guys and they might give the other warrior races something to worry about.

Any weapon: A War Pick and Javelin is listed here but honestly you can equip anything to these bad boys and they’ll find a way to fuck up your vacation into the underground.

Invisibility: Can turn magically invisible until it attacks, casts a spell, or used Enlarge, or concentration is broken for up to one hour.  FOR ONE HOUR.  Just imagine these guys setting up an ambush for up to an hour just waiting to surround you invisibly, and then using Enlarge to pummel everyone in your party while your spell casters are completely useless.  Now that’s a fun creature that any DM can play with.

Some ideas that I pulled out of my ass

1. Use one exiled Duergar as an intro to the Duergar way of live in the underground.  Whether or not you want to have a quest in that direction is one thing, but as party pooping NPC, it would be pretty fun to roleplay
2. Or just go the other way and have the Duergar be exiled because they are the happiest person in existence and the undergrounders couldn’t take it anymore.
3. Duergars are slavers and always looking to add more to their collection as currency and free labor.  Use that as a quest to save a friend, or as a starting point to start your adventurers off in a campaign.  It may seem morally straightforward thing to do, but you can always mix it up by having try to escape but having the chance to save others or themselves and the consequences of those actions.  Maybe they only have seconds to escape while mothers and children are crying out for help but the group unable to do anything or risk being recaptured. Remember, the world is your shithole. Ruin. Everything.
4. If you’re looking for a big plot point, have the group try to stop a Duergar invasion.  They believe in their Manifest Destiny to tyrannically rule everything, this would be an easy moral victory for the group and an easy bad guy to fuck with.  Besides, have you seen the fuckery that Duergars use?  Screamers.  Look it up.
5. If you don’t want to go the whole “big picture” route, have your group go through the underdark, needing passage through one of their cities.  Your group has some roleplay opportunities by attempting to gain passage with the curveball that magic probably wont work and the possible consequences for those actions. I mean, Duergars by nature probably already don’t like them so any means of “attacking” them, and the group would probably be jailed, enslaved, or dead.