Swarm of Poisonous Snakes

The swarm of poisonous snakes can occupy another creature's space and vice versa, and the swarm of poisonous snakes can move through any opening large enough for a Tiny snake. The swarm can't regain hit points or gain temporary hit points.

Melee Weapon Attack: +6 to hit, 0 ft., one creature in the swarm of poisonous snakes's space. Hit: 7 (2d6) piercing damage, or 3 (1d6) piercing damage if the swarm of poisonous snakes has half of its hit points or fewer.
The target must make a DC 10 Constitution saving throw, taking 14 (4d6) poison damage on a failed save, or half as much damage on a successful one.