I've also created stats for the Gear Spirits, creatures of living metal tasked with maintaining the cogs of Mechanus. They basically sound like they've been enslaved by the modrons, and sometimes one just can't stand it anymore and goes walkabout.
Nordom Whistleklik as depicted in the game.
Medium construct, chaotic neutral
Armor Class 17 (natural armor)
Hit Points 52 (7d8+21)
Speed 40 ft.
Str Dex Con Int Wis Cha
16 (+3) 16 (+3) 16 (+3) 16 (+3) 8 (-1) 8 (-1)
Skills Perception +1
Senses truesight 120 ft., passive Perception 11
Languages Common, Modron
Crossbow Expert. Nordom ignores the loading quality of crossbows. Being within 5 feet of a hostile creature doesn’t impose disadvantage on its ranged attack rolls with crossbows.
Disintegration. If Nordom dies, its body disintegrates into dust, leaving behind its weapons and anything else it was carrying.
Multiattack. Nordom makes four fist attacks or four crossbow attacks.
Crossbow. Ranged Weapon Attack: +5 to hit, range 80/320 ft., one target. Hit: 7 (1d8+3) piercing damage.
Fist. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit 5 (1d4+3) bludgeoning damage.
Nordom’s crossbows appear to be normal light crossbows made from metal. They are, however, actually a pair of gear spirits. They have Intelligence and Wisdom scores of 10, are capable to shifting their shape into other sorts of metal weapons and tools, and are able to generate a seemingly infinite amount of ammunition for their crossbow form. The ammunition they create is non-magical. Their metal forms are susceptible to rusting effects, such as the touch of a rust monster. These gear spirits, like Nordom, are rogues and are chaotic neutral in alignment. See below for more details on gear spirits.
Nordom Whistleklik is a rogue quadrone from the plane of Mechanus. Its function became altered after it was exposed to the raw chaos of Limbo. Nordom was encountered by the being known as the Nameless One in the Rubikon, also known as the Modron Maze, on the plane of Limbo. It was inadvertently given its name by the Nameless One when he referred to it as “a backwards modron”. Nordom joined the Nameless One on his quest for a time, and its ultimate fate is unknown. As a rogue modron, its kind are hunting for it so that they may take it back to Mechanus for destruction and replacement.
Nordom has managed to acquire a variety of upgrades, some more visible than others. These upgrades account for its altered stats. Nordom replaced its pair of wings with an extra pair of arms, which allows it to utilize two light crossbows in combat.
Despite it being a rogue, Nordom doesn’t have much more personality than a regular modron. It is still very much a mechanical thinker.
Small construct (shapechanger), lawful neutral
Armor Class 15 (natural armor)
Hit Points 4 (1d6+1)
Move 15 ft., burrow 15 ft.
Str Dex Con Int Wis Cha
10 (+0) 12 (+1) 12 (+1) 10 (+0) 10 (+0) 10 (+0)
Condition Immunities charmed, frightened
Senses truesight 120 ft., passive Perception 10
Challenge ¼ (50 XP)
Meld with Metal. The gear spirit is able to step into any manufactured metal or machinery large enough to fully contain its body. Once fully blended with a machine, it is able to command it to obey its will, though only within the established functions of the device. It could, for instance, make a wheel roll or unlock a door, but it would not be able to make a lamppost attack its enemies. While melded with a metal object, the gear spirit is able to see and hear its environment and it cannot be attacked directly. Destroying the metal object it is melded with forces the gear spirit to be expelled and fall prone into an unoccupied space.
Reduce Armor. If the gear spirit hits a creature wearing nonmagical metal armor or wielding a metal shield with a melee attack, the armor takes a permanent and cumulative -1 to the AC it offers. Armor reduced to an AC of 10 or a shield that drops to a +0 bonus is destroyed. The gear spirit is unable to use this ability with ranged attacks.
Rust Susceptibility. The gear spirit’s body is vulnerable to rust of both natural and magical nature. A successful touch by a rust monster’s antennae removes 1 hit point from the gear spirit, destroying the gear spirit if its hit point total reaches 0. The gear spirit’s body rusts roughly twice as quickly as steel.
Shapechange. The gear spirit is able to change its form, commonly taking the shape of mechanical device or tools. It is able to change its limbs into tools and weapons or assume the form of a weapon at will. It is able to provide itself with near limitless ammunition if it changes all or part of its form into a crossbow.
Crossbow. Ranged Weapon Attack: +3 to hit, range 80/320 ft., one target. Hit: 5 (1d8+1) piercing damage.
Melee Weapon. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. Hit: 3 (1d6) bludgeoning, piercing, or slashing damage depending on weapon form.
Gear spirits are creatures of living metal, assuming a myriad of form. Though it typically takes the form of common tools or mechanical devices, it always has an irregularly shaped face visible. The gear spirits are formed and controlled by the modrons, tasked with the maintaining of the cogs of Mechanus. Each gear spirit is tied to a specific cog by the modrons.
The gear spirit is able to manipulate the shape of its body, taking on a form suitable for whatever task is at hand. It eats manufactured metal, which maintains its form, which is highly susceptible to rusting. The idea of rusting away to nothing is an absolutely horrifying thought for a gear spirit.
Gear spirits have more individuality and personality than modrons do. The servitude forced upon them rankles just a bit, and occasionally a gear spirit will slip away from its duties. Though there is little chance that the unsupervised cog will malfunction, there is still a chance and the modrons hunt down these rogue spirits in much the same way then hunt down rogue modrons. Once they have brought their quarry to Mechanus, a new gear spirit can then be formed to take its place.