Aversion to Fire. If the swarm takes fire damage, it has disadvantage on attack rolls and ability checks until the end of its next turn.
Incessant Gibberish. Any non-gibberling that is within 60 feet of the swarm and doesn't have the deafened condition has disadvantage on Constitution saving throws to maintain concentration on spells and similar effects.
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough to accommodate a Small gibberling. The swarm can't regain hit points or gain temporary hit points.
Multiattack. The swarm makes two Gnashing Teeth attacks.
Gnashing Teeth. Melee Weapon Attack: +6 to hit, reach 0 ft., one target in the swarm's space. Hit:14 (4d4 + 4) piercing damage, or 9 (2d4 + 4) piercing damage if the swarm has half of its hit points or fewer.
A single gibberling is little more than a nuisance—a babbling, hairy creature that darts about, attacking whatever it can find. Unfortunately, gibberlings are rarely encountered alone. They rampage in dense swarms, crawling and leaping over each other to rip, shred, and devour everything in their path.