The NX-3 is a burrowing automaton the size of a shipping container, designed to reshape terrain from beneath the surface. It moves through soil, concrete, and soft rock at a rate of approximately 2 meters per minute, using a combination of thermal boring and mechanical displacement. It does not create tunnels — it liquefies material ahead of it and compresses the slurry behind, leaving no passage. It moves through the earth the way a worm moves through soil, and when it stops, the ground above it is indistinguishable from the surrounding surface.

The Sandcastle's primary function is denial of terrain through subsurface destabilization. It can hollow out the ground beneath a structure, a road, or a defensive position, leaving a thin crust of surface material that appears solid but will collapse under load. An infantry squad walking across a Sandcastle-prepared field drops into a six-meter pit with no warning. A building that has been undermined collapses into its own foundations. A road sinks into a trench that appeared in seconds.

The NX-3 can also bury things. This is the application that has earned it a place on the list of automata that give people nightmares. The unit can position itself beneath a sleeping target, liquefy the ground beneath them, allow them to sink, and resolidify the material above. The process takes less than thirty seconds. The target goes from sleeping on solid ground to encased in hardened earth six meters below the surface. Arcturus documentation describes this as 'non-lethal incapacitation through terrain integration.' Field operatives describe it as being buried alive by a machine you never see.

Survivors — there are survivors, in cases where recovery teams arrive quickly — describe the experience as absolute sensory deprivation. No light, no sound, no movement possible, encased in material that conforms to their body like a mold. The pressure is evenly distributed, so breathing is possible for approximately two hours before CO2 buildup becomes fatal. Two hours of perfect darkness, perfect silence, and the knowledge that you are six meters underground in a coffin made of compressed earth, waiting to find out if anyone knows where you are.