Fey Ancestry. Nar'l has advantage on saving throws against being charmed, and magic can't put the drow to sleep.
Sunlight Sensitivity. While in sunlight, Nar'l has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.
Special Equipment. Nar'l carries a vial containing three doses of eyescratch, a contact poison. A creature that comes into contact with the poison must succeed on a DC 14 Constitution saving throw or be poisoned for 1 hour and blinded while poisoned in this way. A lesser restoration spell or similar magic ends the effect.
Innate Spellcasting. Nar'l's spellcasting ability is Charisma (spell save DC 12). It can innately cast the following spells, requiring no material components:
At will: dancing lights
1/day each: darkness, faerie fire, levitate (self only)
Spellcasting. Nar'l is a 10th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 14, +6 to hit with spell attacks). The drow has the following wizard spells prepared:
Cantrips (at will): mage hand, minor illusion, poison spray, ray of frost
1st level (4 slots): mage armor, magic missile, shield, witch bolt
2nd level (3 slots): alter self, misty step, web
3rd level (3 slots): fly, lightning bolt
4th level (3 slots): Evard's black tentacles, greater invisibility
5th level (2 slots): cloudkill
Staff. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit:2 (1d6 - 1) bludgeoning damage, or 3 (1d8 - 1) bludgeoning damage if used with two hands, plus 3 (1d6) poison damage.
Summon Demon (1/Day). Nar'l magically summons a quasit, or attempts to summon a shadow demon with a 50% chance of success. The summoned demon appears in an unoccupied space within 60 feet of its summoner, acts as an ally of its summoner, and can't summon other demons. It remains for 10 minutes, until it or its summoner dies, or until its summoner dismisses it as an action.
Xanathar's advisor is a nervous and conniving male drow named Nar'l Xibrindas. Nar'l's house was wiped out long ago, but he and his elder brother Soluun survived and joined Bregan D'aerthe. A year ago, Nar'l was given the difficult task of infiltrating the Xanathar Guild and getting as close to the beholder as possible. Not only did he succeed, but in the course of gaining Xanathar's trust, he managed to convince the beholder to eliminate its other advisors. The beholder's paranoia will…