Great Zilla is one of the three skins released in the Skull Temple part of the Jungle Quest offer. It could be purchased as part of an item deal for a limited time in March 2017.
Great Zilla could be purchased for $19.99 in the “Best Deal!” which included the General skin and either 50000 coins (Browser) or 1800 DNA (Mobile). This skin was not available for individual purchase and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.
Note: The Skull Temple sub-offer was released again for a limited time in early June 2019. The Best Deal was lowered to $9.99 and the included coins were reduced to 30000. The package of DNA was no longer an option on either platform.