Boil Beetle Swarm

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 insect. The swarm can't regain hit points or gain temporary hit points.

Frightful Aura. Any creature within 60 feet of the boil beetles when they make a boiling bite attack and are aware of it must succeed on a DC 11 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effects end for it, the creature is immune to the beetle’s frightful aura for the next 24 hours.

Boiling Bite. Melee Weapon Attack: +3 to hit, reach 0 ft., one target 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. The target must make a DC 11 Constitution saving throw, taking 5 (2d4) fire damage on a failed save, or half as much damage on a successful one.

Boiling Burst. When the boil beetles are brought below half their maximum hit points, each creature within 10 feet of it makes a DC 11 Constitution saving throw, taking 5 (2d4) fire damage on a failed save, or half as much damage on a successful one.