Burden of Time. Beasts and humanoids, other than shadar-kai, have disadvantage on saving throws while within 10 feet of the gloom weaver.
Fey Ancestry. The gloom weaver has advantage on saving throws against being charmed, and magic can't put it to sleep.
Innate Spellcasting. The gloom weaver's innate spellcasting ability is Charisma (spell save DC 16, +8 to hit with spell attacks). It can innately cast the following spells, requiring no material components:
At will: arcane eye, mage armor, speak with dead
1/day each: arcane gate, bane, compulsion, confusion, true seeing
Spellcasting. The gloom weaver is a 12th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 16, +8 to hit with spell attacks). It regains its expended spell slots when it finishes a short or long rest. It knows the following warlock spells:
Cantrips (at will): minor illusion, prestidigitation, chill touch, eldritch blast*
1st–5th level (3 slots): armor of Agathys, blight, darkness, dream, invisibility, fear, hypnotic pattern, major image, contact other plane, vampiric touch, witch bolt
*3 beams +4 bonus to each damage roll
Multiattack. The gloom weaver makes two spear attacks and casts one spell that takes 1 action to cast.
Shadow Spear. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit:7 (1d6 + 4) piercing damage plus 26 (4d12) necrotic damage, or 8 (1d8 + 4) piercing damage plus 26 (4d12) necrotic damage if used with two hands.
Misty Escape (Recharges after a Short or Long Rest). When the gloom weaver takes damage, it turns invisible and teleports up to 60 feet to an unoccupied space it can see. It remains invisible until the start of its next turn or until it attacks or casts a spell.
In the perpetual gloom of the Shadowfell lives a society that serves the Raven Queen. They were brought into that dusky realm in ages past, so long ago that they're now perfectly adapted to that cheerless environment, both physically and mentally.