Swarm of Bats

The swarm of bats can occupy another creature's space and vice versa, and the swarm of bats can move through any opening large enough for a Tiny bat. The swarm can't regain hit points or gain temporary hit points.

The swarm of bats can't use its blindsight while deafened.

The swarm of bats has advantage on Wisdom (Perception) checks that rely on hearing.

Melee Weapon Attack: +4 to hit, 0 ft., one creature in the swarm of bats's space. Hit: 5 (2d4) piercing damage, or 2 (1d4) piercing damage if the swarm of bats has half of its hit points or fewer.