I had the cloud heal our android during battle but dismember the rest of the party. Played out well.
Large swarm of Fine constructs, neutral
Armour Class 15
Hit Points 170 (17d10)
Speed fly 40 ft.
Initiative Speed +9 (Dex, Improved Init, tiny)
STR 1 (-8) DEX 18 (+4) CON 10 (+0)
INT 14 (+2) WIS 17 (+3) CHA 19 (+4)
Skills Perception +10
Damage Resistances fire, bludgeoning, piercing, and slashing
Damage Immunities force, necrotic, poison, and psychic
Damage Vulnerabilities lightening
Condition Immunities charmed, frightened, paralysed, petrified, prone, restrained, poisoned, stunned
Senses blindsight 60ft., Darkvision 60 ft., passive Perception 14
Languages Gothic, can only communicate directly with other machines, including androids without special equipment
Challenge 7 (2,900 XP)
Fascination. As an action, a bionanite cloud can create a series of hypnotic waves of color to fascinate creatures within 30 feet. The distraction of a nearby combat or other dangers prevents this ability from working, but otherwise, all affected creatures must succeed at a DC 19 Wisdom save or become fascinated. The bionanite cloud can maintain this effect each round after initial activation as a move action.
Gift of the Machine God. As a creature of technology the cloud gains many damage and condition residences and immunities but they are also susceptible to lightning based attacks.
Reconstructive Healing. As a bonus action or reaction, a bionanite cloud can heal a single living target it shares a space with, healing 1d6 points of damage. The cloud often triggers this ability when it reduces a creature to negative hit points, so as to stabilize the target. The cloud can administer this healing in an instant before resolving any actual damage dealt to prevent a creature’s death from its swarm 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 fine entity. The swarm can’t regain hit points or gain temporary hit points.
Weakness. When a bionanite cloud damages a living creature, it disrupts the transmission of nerve impulses to the creature’s muscles, causing weakness. Mechanically this is represented by the poisoned state. A successful DC 15 Constitution save negates the weakness effect.
Swarm. Melee Weapon Attack: +3 to hit, reach 0 ft., one target in the swarm’s space (large swarm so two targets).
Hit: 25 (5d10) piercing and slashing damage plus weakness, or 15 (3d10) piercing and slashing damage if the swarm has half of its hit points or fewer.
During Combat Once the bionanite cloud notices “defective androids,” it surges up to pacify them. The cloud does not seek to kill these defects, and does not damage foes who have fallen unconscious through damage or poisoning.
Morale The bionanites fight until destroyed, but do not pursue “defective androids” more than 50 feet from the Aurora. If the trap in this room is disarmed, the cloud pursues defective androids throughout the complex. Note that it also treats the mutated androids found deeper in the ship as defective, as well as any other humanoid it encounters.