A group of giant mutant rats. Each one mutated slittly different giving them a different appearence.
The Giant Rats first appeared in New York doing little more then look for food which mostly involved raiding dumpsters, however Zilla Jr. saw them as prey and a group of hunters saw them as a potental trophy. This caused them to attack the hunter and H.E.A.T.. Zilla Jr. then dug into their lair causing it to flood killing all but one. The lone survivor eventually appeared in the Monster Wars under the control of the Tachyons, despite never actually did battle and disappeared after it.
The Giant Rats may be a homage to the unused monster Deutalios do to their rodent appearance, though there is no evidence to support this. They may also play homage to the giant rats in the 1969 film "Latitude Zero".