Bat, Swarm of Bats 2014
CR 1/4 beast
Medium beast, chaotic evil
A creature in the swarm's space that casts a spell with a verbal component must succeed on a DC 12 CON save or the spell fails to cast, expending the action required to cast it but not the spell slot or daily use.
The swarm can't use its keensense while deafened.
The swarm's Perception is 16 when perceiving by hearing.
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 HP or gain temporary HP.
The swarm is resistant to bludgeoning, piercing, and slashing damage, and it is immune to the charmed, frightened, grappled, paralyzed, petrified, prone, restrained, and stunned conditions.
Actions
Melee Weapon Attack: +4 to hit, reach 0 ft., one creature in the swarm's space. Hit: 7 (2d6) piercing damage, or 3 (1d6) piercing damage if the swarm has half of its HP or fewer.
Source: Black Flag SRD (Kobold Press) · License: Creative Commons Attribution 4.0 details