Crawlers (Nanite Cloud)

My PCs recently derailed a whole bunch of my planning through creative play – which is fine, the surprises make the game more entertaining for me this way – they ended up in the Slumbering Ursine Dunes and here are converted monsters for my own reference with abbreviated 5e stat blocks.

Crawlers are 10 or 20-foot square swarms of small cyborg-like beetles, the barge’s clean-up crew.

Large swarm of Fine constructs, unaligned

Armour Class 12, HP 22, Speed fly 40′
Damage Immunities necrotic, poison, and psychic; fire, bludgeoning, piercing and slashing
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 1/2 (10 XP)

Fascination. As an action, a nanite cloud can create a series of hypnotic waves of colour 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 Wisdom save or become fascinated. The nanite cloud can maintain this effect each round after initial activation as a move action.

Swarm 2.0. The swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a Tiny construct. The swarm can’t regain hit points or gain temporary hit points. A swarm takes half damage from attacks that use an attack roll and double damage from effects that require it to make a saving roll. Creatures that are not swarms are impaired while they remain in the swarm’s space or within 5 feet of it and have disadvantage on attack rolls and Constitution saving throws to maintain concentration. The area of the swarm is considered difficult terrain.

Swarm. The swarm attacks all creatures that share a space with it and automatically do 4d4 piercing damage, or 2d4 piercing damage if the swarm has half of its hit points or fewer.