The Plague are the stars of Deadzone. They are the reason the eponymous Deadzone has been created: to form a quarantine zone to prevent their spread and give the corporation time to deal with the threat.
Patient Zero of a plague infection mutates into an enormous creature called a Stage One which attacks anything it sees that is not already infected. Those who survive become Stage Two Plague, heavily mutated but not to the same degree as a Stage One. Those infected by Stage Two Plague become Stage Three. They retain enough of their original identities to use weaponry and pilot vehicles.
I find the progression of the different stages to be a little strange. It seems the Plague weakens as it infects new hosts. Stage Three Plague aren’t contagious. This seems to impair the Plague’s ability to spread. There isn’t a lot of fluff as this race appears to have been created for Deadzone although it is expected that they’ll eventually find their way into Warpath.
Jake Thornton published a version of their faction deck on his website.
The early stages of the Plague are melee only and need to get into combat to be effective. When they do reach melee range they can be scarily effective. Stage One plague fights with 3D8 hitting on 3+ with AP2 talons. This means that he’s very likely to wound an Enforcer in combat and will one-shot them on a regular basis.
Stage Two are only less scary, needing a 4+ to hit with AP1.
Stage Three aren’t really good for much based on their stats, although their special abilities may give them some sort of advantage. These are the footsoldiers of a Plague army and seem to be effective in numbers.