Medium Beast (Swarm), unaligned
Armor Class 12 (natural armor)
Hit Points 22 (5d8)
Speed walk +20, climb +20
Challenge 1/2
Damage Resistances bludgeoning, piercing, slashing
Condition Immunities charmed, frightened, paralyzed, petrified, prone, restrained, stunned
Senses blindsight 10 ft., passive Perception 8
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 insect. The swarm can't regain hit points or gain temporary hit points.
Spider Climb. The swarm can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Web Sense. While in contact with a web, the swarm knows the exact location of any other creature in contact with the same web.
Web Walker. The swarm ignores movement restrictions caused by webbing.
Bites. Melee Weapon Attack: +3 to hit, reach 0 ft., one target in the swarm's space. Hit: 10 (4d4) piercing damage, or 5 (2d4) piercing damage if the swarm has half of its hit points or fewer.
Source: 5e Core Rules · OGL/Open