The Magnavores wanted to steal a train, but needed a diversion. They summoned the hunchbacked rat monster Garganturat to be the diversion. Garganturat kidnapped Heather to keep the Beetleborgs busy. He then shrunk himself and hid in a mousehole dimension where he was finished off by the Beetleborgs' power weapons. He came back twice, once by Vexor's powers in the "Curse of the Shadow Borg." saga where he was one of the victims of Drew's Thunder Stinger (before upgrading to Mega-Blue). He was released again by Nukus during the Season 1 finale.
Drew mentions that he was from issue #113 of the Beetleborgs comic series. Roland also mentioned that Garganturat was born from eating radioactive contaminated cheese mutating him into his monster form in the comic books.