Medium swarm of tiny celestials/fey/fiends, neutral

• Armor Class: 15 (natural armor)
• Hit Points: 40 (5d8 + 15)
• Speed: 30 ft., fly 30 ft. (hover)

• Saving Throws: Dex +5, Con +5
• Skills: Perception +3
• Damage Resistances: Bludgeoning, Piercing, Slashing
• Damage Immunities: Psychic
• Condition Immunities: Charmed, Frightened, Grappled, Paralyzed, Petrified, Prone, Restrained, Stunned
• Senses: Darkvision 60 ft., Passive Perception 13
• Languages: Understands the languages you speak but can’t speak
• Challenge: 3 (700 XP)

Features

Swarm:
The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny creature. The swarm can’t regain hit points or gain temporary hit points.

Actions

Bite (Swarm):
Melee Weapon Attack: +5 to hit, reach 5 ft., one target.
Hit: 18 (4d6 + 3) piercing damage, or 9 (2d6 + 3) piercing damage if the swarm has half of its hit points or fewer.

Buzzing Agitation (Recharge 5-6):
The swarm buzzes loudly around a creature it shares a space with. That creature must succeed on a DC 13 Wisdom saving throw or be stunned until the end of its next turn.

Swarm Surge:
As a bonus action, the swarm can move up to half its flying speed without provoking opportunity attacks.