Umbral Sprite Swarm
Medium fey humanoid (swarm)
Level 4 Controller XP 175

Initiative +6        Senses Perception +8; blindsight 6
Swarm Attack aura 1; each enemy that starts its turn within the aura takes 3 damage.
HP 55; Bloodied 27
AC 18; Fortitude 15, Reflex 17, Will 15
Resist half damage from melee and ranged attacks; Vulnerable 5 against close and area attacks
Speed 4, fly 6 (hover)

(⚔) Swarm of Fangs and Blades (standard, at-will)

+10 vs AC; 1d6+4 damage .

ᗕ Darkwave (standard, recharge ⚄⚅) ✦ Necrotic, Zone

Close burst 3; +8 vs Reflex; 2d8+4 necrotic damage. Effect: The burst creates a zone of darkness that lasts until the end of the umbral sprite swarm's next turn. The zone blocks line of sight.

Fade Away (immediate reaction, when the umbral sprite swarm takes damage; encounter) ✦ Illusion

The umbral sprite swarm is invisible until after it hits or misses with an attack or until the end of its next turn.

Alignment Unaligned        Languages Elven
Skills Stealth +11
Str 8 (+1)      Dex 18 (+6)      Wis 13 (+3)
Con 15 (+4)      Int 13 (+3)      Cha 15 (+4)

Published in Monster Manual 2, page(s) 194.