Abaddon's Locusts (5e Creature)
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Gargantuan swarm of tiny fiends, neutral evil
Damage Resistances bludgeoning, piercing, slashing
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 locust. The swarm can't regain hit points or gain temporary hit points.
Drone of Destruction. Any creature that starts its turn in the swarm's space must make a DC 23 Constitution saving throw, taking 35 (10d6) thunder damage on a failed save or half as much on a successful one.
Multiattack. The swarm makes ten attacks: eight with its bites and two with its stingers.
Bites. Melee Weapon Attack: +13 to hit, reach 0 ft., one creature in the swarm's space. Hit: 34 (12d4 + 4) piercing damage, or 19 (6d4 + 4) piercing damage if the swarm has half of its hit points or fewer.
Stingers. Melee Weapon Attack: +13 to hit, reach 0 ft., one creature in the swarm's space. Hit: 19 (6d4 + 4) piercing damage, or 11 (3d4 + 4) if the swarm has half of its hit points or fewer, and the target must make a DC 23 Constitution saving throw. On a failed save, the target becomes poisoned for 150 days.
When a council of deities (or an overdeity) deems that a world should end, many swarms of these horrors are brought forth from the lowest depths of the Abyss, down to strip the lands clean of life.