Clockwork Bat

Lesser Pack Tactics. The creature gains advantage on attack rolls made against a target when 3 allies are within five feet of the target and none of the allies are incapacitated

Shrill Screech. The bat emits a harsh scraping sound. Other bats within 50 feet that can hear can use a reaction to join in. The effect differs on the amount of bats joining; 1-2 - nothing happens.  3-5 - Any creatures that can hear within 30 feet are deafened for 30 seconds. 6-8 - Any creatures that can hear within 30 feet are deafened for 1 minute and take 2d4 thunder damage. The damage increases by 1d4 for every 4 bats over 8.

Claws. Melee Weapon Attack: +2 to hit, reach 5 ft., 1 target. Hit: 4 (1d6) [slashing] damage. 

Shrill Screech (reaction). The bat uses its reaction to join in on a Shrill Screech. If it uses its reaction in this way, it cannot use its action this round to perform a Shrill Screech.