It’s not that big. Well, actually it’s quite small, but the fierce nature of Goofzilla compensates for the lack of size which would be capable of destroying whole cities.
The Goofzilla Minipet DLC unlocks the Goofzilla epic minipet (+3% critical hit chance, Combat is even more bloody), a friendly monster that you can't get rid of. You will also receive a rare item: The Xenofiend Helmet.