Gargantuan Swarm of Medium aberrations, Chaotic Evil
Armor Class 18 Natural
Hit Points 188 (32d8 + 64)
Speed 40 ft., hover
STR
1 (-5)
DEX
25 (+7)
CON
15 (+2)
INT
10 (+0)
WIS
15 (+2)
CHA
16 (+3)
Saving Throws DEX +13
Skills Perception +6
Damage Resistances Fire
Damage Immunities Acid, Cold, Lightning, Necrotic, Poison, Psychic, Thunder; Bludgeoning, Piercing, and Slashing from Metal Weapons
Senses Passive Perception 16
Languages Common Understands but cannot speak
Challenge 18 (20,000 XP)
Proficiency Bonus +6
Traits

Swarm. The swarm can occupy another creature's space, and other creatures can enter the swarm's space, the swarm's area counts as difficult terrain and for every 5 feet moved inside of the swarm deals 1d10 lightning damage to the creature. 

Strength in Numbers. The swarm has advantage on Strength, Dexterity, and Constitution saving throws as long as it has at least half of its hit points remaining.

Electrosensative. The swarm automatically knows the location of a creature within 1 mile of it that is carrying at least 10 lbs of unconcealed metal.

Actions

Multiattack. The Arc-Storm makes three storm flurry attacks, or two lightning arc attacks.

Storm Flurry. Melee Weapon Attack: +11 to hit, range 5 ft., 1 target. Hit: 19 (3d8 + 7) lightning damage or 11 (1d8 + 7) lightning damage if the swarm has less than half of its hit points remaining.

Lightning Arc. Ranged Weapon Attack: +11 to hit, range 30 ft., 1 target. Hit: 22 (5d6 + 7) lightning damage or 10 (1d6 + 7) lightning damage if the swarm has less than half of its hit points remaining, on a hit, the lightning jumps to another target within 10 feet of the initial target, making another attack roll for the new target.

Stormcall (Recharge 5-6). Roll a d6 for each creature inside or within 10 feet of the Arc-Storm, for each 5 and 6 rolled the respective creature is struck by lightning, making a DC 17 Dexterity saving throw, taking 20 (4d10) lightning damage or half as much on a success. For each other creature not struck must make a DC 15 Constitution save, taking 12 (3d8) thunder damage or half as much on a success.

Description

An Arc-Storm occurs when several dozen Arc-Ghosts converge on one point, the reason is speculated to be possibly due to particularly high magical or spiritual energy. Regardless, an Arc-Storm is among one of the most deadly events that one could encounter in the wasteland. The area around an Arc-Storm is a massive lightning storm, harmless to the Arc-Storm, but quite deadly to anyone caught in the area, the host itself is a menace as well, getting caught inside the mass of semi-corporeal bodies means certain death. Moral of the story, avoid at all costs.

Lair and Lair Actions

The area around an Arc-Storm is considered its "lair" and moves with the host. The lair is pointedly marked by a massive lightning storm.

Lair Actions

On initiative count 20 (losing initiative ties), the [monster name] takes a lair action to cause one of the following effects; the Arc-Storm can’t use the same effect two rounds in a row:

  • Lightning strikes a creature that the Arc-Storm can see within 60 feet of it, the creature must make a DC 17 Dexterity saving throw taking 20 (4d10) lightning damage or half as much on a successful save.
  • A massive thunderclap sounds overhead, every creature that can hear within 120 feet of the Arc-Storm must make a DC 15 Constitution saving throw or be deafened for 1 minute, remaking the save at the end of each of their turns, ending the effect on themselves on a successful save.

Regional Effects

The region containing an Arc-Storm is a lightning storm.

  • The area in a 1-mile radius around the Arc-Storm experiences constant static interference, creatures with metal armor or weapons may experience static shocks and may be prone to lightning strikes.
  • Weather effecting spells and abilities such as Skywrite, Control Weather, or Storm Sorcerer's storm guide ability have difficulty affecting the lightning storm. A creature attempting to do so must make a spellcasting ability skill check contested by a Charisma check from the Arc-Storm. On a success, the spell or ability takes effect, on a fail the attempt is wasted along with any spell slots involved.

If the Arc-Storm is dispersed, these effects fade over the course of 1d4 hours.

KallmeKilo

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