The ondroni /ˈɑndroʊni/ is a gigantic grey stranger. Its eight black limbs fade to red at the hands and feet, and its fingers and toes are black and white, matching the patterning around its mouth, within its eye markings. There is no elasticicity to its artificial skin, and the "flesh" beneath is spongy – like the external surface and internal stuffing to a carnival ride seat. The metal teeth are coated with a white substance nearly similar to tooth enamel; this is the only part of the ondroni's body capable of regeneration.

The ondroni's "animatronic"^Ⴠ insides consist of train and automobile parts, scrap metal fragments, screws, and industrial frames. No two ondroni possess the same mixture.

The ondroni's deep, rumbling voice shakes the ground around it. Unless sped up one hundred times, this droning cadence cannot be recognized as speech. Once sped up, its mechanical voice becomes discernible, if clanking and mechanical. Its language consists of few repetitions; individual "words" may be millions – if not billions – of syllables long.

The ondroni appears deep underground, and always at least 127 feet beneath the deepest architectural structure within a city. It prefers dry, rocky earth, and does not generate in excessively wet soil. When it first appears, it is as small as a pebble, and lacks its internal armature, which develops organically as the ondroni increases in size over the next one to eight decades. During formation, it lets out periodic bellows, which break apart the nearby rocks and dirt to enlarge the tomb and allow the stranger to grow. Once the ondroni is fully-formed, it tunnels out of this cavity and begins its life.

The ondroni possesses a cold, mechanical disposition. It moves with the jagged motions of an old construction vehicle, and spends its days moving earth and rocks with meticulous precision to create smooth-walled tunnels with flat floors. It possesses incalculable strength, and has no difficulty using its palm to break apart solid rock. The ondroni's tunnels are arranged in a uniform grid that correspond to the earth's longitudinal and latitudinal lines. Although the ondroni is does not engage in social interactions with others of its strain (and, in fact, seems to avoid other strangers in general), populations within a city always contribute towards expansion of the same grid, and occur at the same depth as one another.^Ꝺ

Any duration of activity is followed by an equal duration of dormancy. While dormant, the ondroni stands completely still, its head held low and its limbs drooping, and does not respond to any external stimuli.

Owing to the depth of the ondroni's tunnels, there is little, if any, potential physical interaction between a sensitive and ondroni. Although the ondroni remains inert while in a dormant state – and can be destroyed completely by a persistent sensitive – active ondroni use their great strength to pick up, crush, and fold any nearby sensitive into the lining of the tunnel walls. Other ondroni shudder and smile while walking through these "pasted" sections, but otherwise, this stranger remains disinterested in either individual people, or greater human activity.^Ԅ

The internal flesh on an ondroni's corpse breaks apart into asbestos sand, which scatters to leave behind a pile of rusted metal. Other ondroni press tight handfulls into the walls, then continue on, forever in construction of their unseen infrastructure.