So it turns out the third army will be ... the First Lantern? Ok, I am not too impressed that thematically to replace the GL corps the Guardians settle for ancient technology. This brain bug might work with fantasy theme stories, but I irritates me somewhat in sci fi settings. I mean, older technology might work if its by some other ancient race, but the technology is ancient technology from the same race.
That being said, the first army can reproduce itself like a Von Neumann machine but requiring the bodies of sentients, where they rewrite your DNA. One wonders why they need existing organics, as opposed to replicating it from general matter, but I guess this has a more greater horror aspect to it, as the sentient is mindwiped, and altered into a soldier for the third army. Its not quite clear if this replicating power is from the first lantern, or simply that the Guardians are using the first lantern as a power battery (which the latter accuses them of doing). However it makes sense. Its hard for Black Hand to bring the dead back to life when their "organic matter has been completely rewritten" and their "mind broken down and decimated". The heart also gets discarded similar to how the Red Lanterns do it, so even if you reverse most of the process, the sentient will most probably die without a heart.
Anyway, I am looking forward to seeing how the corps deal with the third army, but if LO3W is any indication, only Sodom Yat will remain and most of the corps will be weaken.