Swarm of Centipedes
Medium Beast (Swarm), unaligned
100 XP
Special Abilities
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.
Actions
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.
A creature reduced to 0 hit points by a swarm of centipedes is stable but poisoned for 1 hour, even after regaining hit points, and paralyzed while poisoned in this way.
Quick Reference
Running This Encounter
The swarm moves as a writhing mass, attacking all creatures within 5 feet. Use the swarm's Swarm trait to emphasize that it cannot be targeted by single-target spells and that damage reduction only applies once per turn. Position the swarm to split the party or force them into difficult terrain where escape is limited. Describe the unsettling sound and sight of dozens of chittering legs to build atmosphere.
Combat Tactics
The swarm pursues the weakest or most isolated party member, using its speed (40 ft.) to control positioning. It prioritizes staying within melee range and will surround targets when possible, preventing opportunity attacks as creatures flee. The swarm fights to the death, having no sense of self-preservation.
Environment & Setting
Giant centipedes swarms inhabit dark, damp places: underdark caverns, dungeon corridors, overgrown ruins, or dense swamps. They nest in crevices and emerge from holes or walls, creating ambush opportunities.