Praetorians (Mass Effect)

Hovering tanks resembling a cross between a octopus and a giant crab, praetorians are well-armored killing machines of mysterious origins.

Praetorians employ redundant systems from the multiple humans encased within them. Armed with eye-mounted particle beams, they are capable of unleashing devastating close-range energy attacks that also regenerate their shields. Within hours after death, the organic components of praetorian corpses disintegrate into a denatured pus, while their mechanisms turn to ash. One specimen, autopsied within minutes of death, reveals a clue: nanomachines may disintegrate the praetorian's organic and mechanical components before self-destructing.

If correct, this self-rendering hypothesis could account for three documented cases of dead praetorians apparently releasing (or becoming) clouds of neurotoxic gases, causing suffocating paralysis and nearly-instant death. In one remote facility, 17 soldiers died from gas inhalation while assessing the praetorian. Any personnel in the vicinity of dead praetorians are urged to protect themselves with breathing apparatus.