Death Butterfly Swarm

Demon-Haunted. A death butterfly swarm results when a rare breed of carrion-eating butterflies, drawn to the stench of great decay, feeds on the corpse of a fiend, demon, or similar creature. Dizzying and Poisonous. The colorful and chaotic flapping of the insects’ wings blinds and staggers those in its path, allowing the swarm to necrotize more flesh from those it overruns. Attracted to rotting material, the swarm spreads a fast-acting, poison on its victims, creating carrion it can feed on immediately. Devour the Undead. Undead creatures are not immune to a death butterfly swarm’s poison, and a swarm can rot an undead creature’s animating energies as easily as those of the living. Given the choice between an undead and living creature, a death butterfly swarm always attacks the undead. Such swarms find ghouls and vampires particularly appealing. Some good-aligned forces regard summoning these swarms as a necessary evil.

Traits

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Potent Poison: The death butterfly swarm’s poison affects corporeal undead who are otherwise immune to poison.
Swarm: he swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Tiny insect. The swarm can’t regain hit points or gain temporary hit point.
Weight of Wings: A creature in a space occupied by the death butterfly swarm has its speed reduced by half, and must succeed on a DC 13 Dexterity saving throw or become blinded. Both effects end when the creature doesn’t share a space with the swarm at the end of the creature’s turn. If a creature succeeds on the saving throw, it is immune to the swarm’s blindness (but not the speed reduction) for 24 hours.

Actions

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Multiattack: The swarm makes a Bite attack against every target in its spaces.
Bites (More than half HP): Melee Weapon Attack: +3 to hit, range 0 ft., Every target in the swarm's space. Hit: 22 (6d6 + 1) piercing damage plus 10 (3d6) poison damage. The target becomes poisoned for 1d4 rounds; a successful DC 13 Constitution saving throw reduces poison damage by half and prevents the poisoned condition.
Bites (Half or less HP): Melee Weapon Attack: +3 to hit, range 0 ft., Every target in the swarm's space. Hit: 11 (3d6 + 1) piercing damage plus 10 (3d6) poison damage. The target becomes poisoned for 1d4 rounds; a successful DC 13 Constitution saving throw reduces poison damage by half and prevents the poisoned condition.

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Tome of Beasts

Death Butterfly Swarm CR: 4

Large large swarm of tiny insects, chaotic/evil

Armor Class:

Hit Points: 80

Speed: 5 ft. , fly: 40 ft. , can hover

STR

1 -5

DEX

13 +1

CON

10 +0

INT

1 -5

WIS

12 +1

CHA

15 +2

Damage Vulnerabilities: cold, fire

Damage Resistances: bludgeoning, piercing, slashing

Condition Immunities: charmed, frightened, paralyzed, petrified, prone, restrained, petrified

Senses:

Darkvision 60 ft., passive Perception 11

Languages: -

Challenge Rating: 4 ( 1100 XP)

Proficiency Bonus: +2

Actions

Multiattack. The swarm makes a Bite attack against every target in its spaces.

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Bites. Melee Weapon Attack: +3 to hit, reach 0 ft., every target in the swarm’s space. Hit: 6d6+1 piercing damage, or 3d6+1 piercing damage if the swarm has half of its hit points or fewer. The target also takes 3d6 poison damage, and becomes poisoned for 1d4 rounds; a successful DC 13 Constitution saving throw reduces poison damage by half and prevents the poisoned condition.