Cleric of the Swarm

Multitudinous Mind. The Cleric of the Swarm has advantage on Concentration saving throws when it has more than half HP.

Spiteful Death. When a creature reduces the Cleric of the Swarm to 0 HP with a melee attack, the creature is affected by the spell contagion as if the Cleric of the Swarm had hit it with the melee spell attack, with the disease chosen at random.

Spellcasting. The Cleric of the Swarm is a 11th-level spellcaster. Its spellcasting ability is [Wisdom] (spell save DC 17, +9 to hit with spell attacks). The Cleric of the Swarm has following Cleric spells prepared:
Cantrips (at will): toll the dead, thaumaturgy
1st level (4 slots): command, inflict wounds, sanctuary
2nd level (3 slots): calm emotions
3rd level (3 slots): dispel magic, life transference, water walk
4th level (3 slots): locate creature,
5th level (2 slots):commune, contagion, insect plague
6th level (1 slot): word of recall
*The Cleric of the Swarm casts water walk on itself before combat.

Action inflict wounds. Melee Spell Attack: +9 to hit, reach 5 ft., 1 target. Hit: 3d10 (3d10 + 1d10 for every spell slot above 1st) [necrotic] damage.