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 raven. The swarm can't regain hit points or gain temporary hit points.
Actions
Beaks. Melee Weapon Attack: +4 to hit, reach 5 ft., one target in the swarm's space. Hit: 7 (2d6) piercing damage, or 3 (1d6) piercing damage if the swarm has half of its hit points or fewer.