Swarm of Rats

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.

The swarm has advantage on Wisdom (Perception) checks that rely on smell.

+0 to hit. Hit: 5 ((2 - (@statuses.bloodied))d6) piercing damage. Melee Weapon Attack: , 0 ft., one creature in the swarm's space. Hit: damage, or damage if the swarm has half of its hit points or fewer.