One of many specialised castes of cyborg warriors available to the Adeptus Mechanicus, the Pteraxii are optimised for instinctive reaction and agility. Pteraxii’s reflexes are accentuated by paring back elements of cogitation that impede their primary function. Implanted with additional limbstumps – scapuli superior – on their back, a flight pack of thrusters and reactive life surfaces is connected to them. The flight packs become part of the Pteraxii, who serve in several roles. Skystalkers find optimal vantage points from which to pick off their targets – whether isolated battlefield marks or feral psyber familiars and servo-cherubim – with flurries of razor-sharp flechettes.

Pteraxii Skystalkers are armed with flechette carbines, enabling them to unleash a withering storm of solid shot at their enemies from a safe distance. The unit's Alpha is instead equipped with a flechette blaster and taser goad. They offer superb anti-infantry fire support, but they also carry braces of arc grenades which they can drop among the enemy as they soar overhead.