Homebrew
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a medium mechanical angel. The swarm can't regain hit points or gain temporary hit points.
Multiattack. The swarm makes two morningstar attacks. Morningstars. Melee Weapon Attack: +9 [1d20+9] to hit, reach 0ft, one creature in the swarm's space. Hit: 11 (1d8+7) 1d8+7 piercing damage.