This animal appears in the Monster Manual (2024).
Traits
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 snake. The swarm can’t regain Hit Points or gain Temporary Hit Points.
Actions
Bites. Melee Attack Roll: +6, reach 5 ft. Hit: 8 (1d8 + 4) Piercing damage—or 6 (1d4 + 4) Piercing damage if the swarm is Bloodied—plus 10 (3d6) Poison damage.