Tome of Magic
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 crow. The swarm can't regain hit points or gain temporary hit points.
Beaks. Melee Weapon Attack: +4 To Hit, Reach 5ft, One Target in the swarm's space. Hit: 6 (2D6) Piercing Damage, or 3 (1D6) Piercing Damage if the swarm has half of its Hit Points or fewer.