Swarm of Rats
Medium Beast (Swarm), unaligned
50 XP
Special Abilities
Keen Smell
The swarm has advantage on Wisdom (Perception) checks that rely on smell.
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 rat. The swarm can't regain hit points or gain temporary hit points.
Actions
Bites
Melee Weapon Attack: +2 to hit, reach 0 ft., one target in the swarm's space. Hit: 7 (2d6) piercing damage, or 3 (1d6) piercing damage if the swarm has half of its hit points or fewer.
Quick Reference
Running This Encounter
A swarm of rats attacks as a single entity with 24 hit points, using its Bite attack that targets one creature per turn. The swarm can occupy the same space as other creatures and move through spaces as small as 1 foot wide. Control the swarm's movement to surround and isolate weaker party members, and remember it has advantage on Wisdom (Perception) checks relying on smell. Describe the visceral horror of dozens of chittering rats clawing and biting to create atmosphere despite the low individual threat.
Combat Tactics
The swarm prioritizes isolated targets and those already damaged, using hit-and-run tactics by moving through difficult terrain or tight spaces where larger creatures cannot follow. It will attempt to surround casters and split the party's attention. The swarm flees if reduced below 10 hit points, scattering into walls or sewers.
Environment & Setting
Urban sewers, abandoned cellars, grain stores, or cluttered dungeons filled with rubble and tight spaces that restrict larger creatures. Ideal locations include areas with multiple exits and vertical terrain where the swarm can escape.