Plague Eaters are somewhat horrible opposites of Virophages and Bile Launchers. First, they're mobile. Second, instead of infesting they eat the infested.

Arctic Zerg Roaches are greatly tactical in one point as offensive units among defensive Zergs Brood. They literally freeze enemy units with freeze breath they got thanks to evolving by living on extremally low temperatures.

(Zerg Roach belongs to Blizzard)