Swarm of Spectre Bats
Traits
Echolocation. The swarm can’t use its blindsight while deafened.
Keen Hearing. The bat 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.
Incorporeal Movement. The swarmcan move through other creatures and objects as if they were difficult terrain.
Sunlight Sensitivity. While in sunlight, the swarm has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.
Actions
Life Drain Bite. The swarm attacks with its Bite.