• Echolocation: The swarm can't use its blindsight while deafened.
• Keen Hearing: The swarm has advantage on Wisdom (Perception) checks that rely on hearing.
• 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 bat. The swarm can't regain hit points or gain temporary hit points.
• Bites: Melee Weapon Attack: +4 to hit, reach 0 ft., one creature in the swarm's space. Hit: 5 (2d4) piercing damage, or 2 (1d4) piercing damage if the swarm has half of its hit points or fewer.