In the years following the Brood War, Kerrigan became obsessed with the genetic codes of species with hyper-regenerative properties. The most impressive example was the unassuming acidic Zantar Slug living in the humid, mountainous depths of Garrxax. This tiny slug was capable of healing itself at rapid rates, and it also excreted mucus that could eat through neosteel. Consequently it was quickly assimilated into the Swarm. Thus the Roach was evolved, a creature that can heal itself rapidly and deliver deadly ranged acid blasts. In a one-on-one battle, not much can stand against this regenerating monstrosity.