HAOS was a gargantuan creature appearing as a centipede-like cephalopod, with large and small tentacles lining its lower half body. Its origins, however, are unknown due to the presence of a human-like face. It was seen to emerge from a chrysalid, making it a Complete Mutant.
It was incredibly resilient to gunfire and to injury in general. It seemed to have a weakness to electricity, because a recently mutated Piers Nivans attacked it with electricity, which allowed it to be injured. When it was injured, it tended to go to a safe place and form another chrysalid around it, to heal its wounds. This added to its resilience to injury and made it extremely tough to kill.
It was incredibly flexible. Its limbs looked more like tentacles than traditional limbs, which may suggest that there may also be cephalopods involved in its creation. HAOS was at a mere 70.3% of its incubation at the moment of its release. Even at this incomplete form it proved to be a great threat against seasoned BSAA officers. HAOS was at such a critical stage of metamorphosis that its translucent skin might have been a defect from its incomplete transformation. Its maximum height would be about the same as a 20-story building
HAOS appears to have the ability to change its own mass depending on the situation it finds itself in. If Haos finds itself in an area too small for its gigantic body, it will transform into a chrysalid, and condense itself into a smaller version. HAOS also appears to have the ability to grow rapidly in size when given enough time. Haos' ability to heal its own wounds, and change mass at any given time could make it one of the most resilient B.O.W.s.
Like a Rasklapanje, when injured, HAOS' lower half can detach from its upper half and pursue Chris and Piers independently.