AD&D Derroes roughly adapted to 5th edition....

Another experiment in 5th edition design. This time, at least, I crack open the Monster Manual II rather than the Fiend Folio. The Derroes, while they seem to be too much like the Duergar, are actually a major reference to Richard Sharpe Shaver's insane conspiracy rantings. I needed to come up with something menacing in my game, and the weirdness of the Shaver Mystery seemed like a good way to sneak in some weirdly menacing creatures conspiring against and experimenting on humanity into the campaign to fill in an element of a character's background he left open for me to fill.

Some statements from the MMII about the derroes:

The derro are a degenerate race of dwarf-like stature, possibly a cross between evil humans and dwarves. They inhabit the great subterranean realms common to drow and their ilk (kuo-toans, mind flayers, troglodytes, etc.). Although the derro hate light and suffer from nausea in sunlight, they venture out upon the surface of the earth at night through secret shaft openings to steal and kidnap humans for slaves. Rumor says that some humans are actually eaten as well....

The derroes are said to have a major stronghold somewhere deep beneath the ground, and there their savants plot and scheme to devastate the upper world and enslave all mankind.... They speak a language of their own, some Common, and know the trade vernacular of the underground world.

Derroes are very much like humans, only shorter and slightly more muscular in proportion to their height. Their features tend towards grossness. Their hair is pale tan or yellow, their skin is very white with a bluish undertone, and their eyes are very large. (p. 42)

I see them as terrible secretive and inscrutable sociopaths with a desire to torture, experiment, and dominate. Shaver said his dero meant "detrimental robots", though they weren't robots in the common sense that they were actual machines, but that they lacked any sort of real humanity.

Derro
Medium humanoid, chaotic evil
Armor Class: 15 (Studded leather)
Hit Points: 33 (6d8+6)
Speed: 30ft
STR 10 (+0), DEX 16 (+3), CON 14 (+2), INT 14 (+2), WIS 14 (+2), CHA 8 (-1)
Skills:  Perception +5, Stealth +6
Senses: Darkvision 120 feet, passive perception 15
Languages: Undercommon, limited common, Derro

Sunlight Sensitivity: While in sunlight, the derro has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Magic Resistance: Derro have advantage to saves vs. spells and magical effects.

Actions

• Repeating Crossbow: ranged weapon attack +6, range 30/120 feet, one target. Hit 1d4 plus save (CON DC 11) or 2d6 poison damage. 10 shot magazine.
• Hook Fauchard: melee weapon attack +6, one target. Hit 1d4+3 plus save (DEX DC 11) or knocked prone.
• Dagger: melee weapon attack +6, one target. Hit 1d4+3 plus save (CON DC 11) or 2d6 poison damage.

Derro Savant
Medium humanoid, chaotic evil
Armor Class: 15 (Studded leather)
Hit Points: 33 (6d8+6)
Spd: 30ft
STR 10 (+0), DEX 16 (+3), CON 14 (+2), INT 16 (+3), WIS 14 (+2), CHA 8 (-1)
Skills:  Arcana +6, Investigation +6, Medicine +5, Perception +5, Stealth +6
Senses: Darkvision 120 feet, passive perception 15
Languages: Undercommon, limited common, Derro

Sunlight Sensitivity: While in sunlight, the derro has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Magic Resistance: Derro have advantage to saves vs. spells and magical effects.

Spellcasting: The Derro Savant is a 9th level spellcaster, Its spell casting ability is Intelligence (spell DC 14, spell attacks +6). The savant has the following spells prepared:

• Cantrips (at will):  Blade Ward, Mage Hand,  Minor Illusion, Prestidigitation
• 1st level (4 slots): Charm Person, Comprehend Languages, Detect Magic, Witch Bolt
• 2nd level (3 slots): Phantasmal Force, Suggestion
• 3rd level (3 slots): Blink, Fear
• 4th level (3 slots): Dimension Door, Phantasmal Killer
• 5th level (1 slot): Modify Memory

Actions

• Dagger: melee weapon attack +6, one target. Hit 1d4+3 plus save (CON DC 11) or 2d6 poison damage.