Gas zombies are zombies that have mutated from the gas unleashed upon Fortune City by Phenotrans, granting them increased speed and strength over regular zombies, and the ability to project blood at their enemies. It is unknown how the gas strengthens the zombies, but it most likely causes some kind of chemical reaction with the queens inside a zombie's body, causing mutation. It was invented to mature queens at a faster rate for harvest, due to the large quantity required to make Zombrex.