Cultist Footsoliders

Martial Advantage. Once per turn, the swarm can deal an extra 7 (2d6) damage to a creature it hits with a weapon attack.

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 creature. The swarm can’t regain hit points or gain temporary hit points and is immune to any spells that aren't AOE.

Stampede. When the swarm moves through the space of a creature Large or smaller, it must succeed on a DC 13 strength check or be knocked prone.

Multiatack. The swarm makes four attacks with its longsword , or two attacks with its longsword if it has half of its hit points or fewer. 

Glaive. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (1d10 + 1) slashing damage, or 6 (1d10 + 1) slashing damage if used with two hands.

Volley. The swarm launches a volley of arrows at a point 150/600 ft of it. Each creature in a 10 foot radius sphere centered on that point most make a DC 13 Dexterity saving throw. On a failed save, a creature takes 20 (4d8+1) points of piercing damage or 10 (2d8+1) points of piercing damage if the swarm has half of it's hit points or fewer. On a successful save, it takes half as much damage. 

Reactive. A swarm can make four reactions, or two reactions if it has half or fewer of its hit-points.