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 creature. The swarm can't regain Hit Points or gain Temporary Hit Points.
Swarm of Proboscises. Melee Attack Roll: +5, reach 5 ft. Hit:14 (2d10 + 3) Piercing damage, or 8 (1d10 + 3) Piercing damage if the swarm is Bloodied. If the target is a Medium or smaller creature in the swarm's space, the target has the Grappled condition (escape DC 13). Until the grapple ends, the target takes 7 (2d6) Necrotic damage at the end of each of its turns.
Notorious, Clinging Bloodsuckers