Writhing Shadows. The Writhing Darkness can instantly Teleport from any shadow to another within 60ft.

Spellcasting. The Writhing Darkness is a spellcaster. Its spellcasting ability is Intelligence (spell save DC 18, +14 to hit with spell attacks). The Writhing Darkness has following Wizard spells prepared:
Cantrips (at will): Chill Touch, Infestation, Mind Sliver, Poison Spray, Toll The Dead, 
1st level (6 slots): Cause Fear, Chromatic Orb, Expeditious Retreat, False Life, Fog Cloud, Hideous Laughter, Magic Missle, Shield, Sleep,
2nd level (6 slots): Acid Arrow, Blindness/Deafness, Blur, Crown Of Madness, Darkness, Enlarge/Reduce, Mind Spike, Mirror Image, Misty Step, Phantasmal Force, Shadow Blade, Shatter, Suggestion, Tasha's Mind Whip,
3rd level (5 slots): Animate Dead, Blink, Counterspell, Dispel Magic, Enemies Abound, Fear, Feign Death, Fireball, Slow, Spirit Shroud, Summon Shadowspawn, Vampiric Touch,
4th level (5 slots): Blight, Confusion, Greater Invisibility, Hallucinatory Terrain, Phantasmal Killer, Raulothim's Psychic Lance, Vitriolic Sphere,
5th level (4 slots): Cloudkill, Danse Macabre, Dominate Person, Enervation, Immolation, Mislead, Negative Energy Flood, Synaptic Static, Wall Of Force,
6th level (4 slots): Chain Lightning, Circle Of Death, Disintegrate, Eyebite, Flesh To Stone, Globe Of Invulnerability, Mental Prison, Scatter,  

Multi Attack. The Writhing Darkness makes three attacks two with either its claws or shadow dart and one with its stinger tail. Alternatively it can cast two spells provided one is an action and the other can be cast as a bonus action. 

Claws. Melee Weapon Attack: +12 to hit, reach 10 ft., 1 target. Hit: 13 (3d4 + 4) [Necrotic] damage. 

Shadow Dart. Ranged Weapon Attack: +12 to hit, range 120/300 ft., 1 target. Hit: 14 (2d8 + 4) [Necrotic] damage.

Stinger Tail. Melee Weapon Attack: +12 to hit, reach 10 ft., 1 target. Hit: 7 (2d4 + 4) [Piercing] damage. Target must make a DC 18 CON save or become poisoned and take 6 (1d6 + 3) [Poison] Damage

Consume Darkness: As A bonus action the Writhing Darkness can consume a persons shadow to regain health, Melee Weapon Attack, +10 to hit. reach 10ft. Hit: 16, (1d10+8) Necrotic Damage. The Writhing Darkness heals for damage done. A shadow consumed this way can only be regained by a greater restoration or a wish spell. The Writhing Darkness cannot consume the shadow of a person who no longer has one.

Opportunity Attack. When an enemy moves out of the writhing shadows melee or ranged attack reach it can make an attack of opportunity against the target.

Magic Born. Once per combat The Writhing Darkness can instantly counterspell without expending a spell slot any one spell cast within 120ft of it.

Creature Of The Dark. On initiative count 20 the Writhing Darkness can cast Darkness centered on itself without expending a spell slot or needing concentration.

Psychic Horror. The Writhing Darkness unleashes a banshee like scream forcing everyone within 100ft to make a DC 18 WIS save or take 8d8 Psychic Damage, once used must roll a 6 on a 1d6 to recharge.

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