Leviathan is one of the skins released in the monthly Titans Skin Collection. It could be purchased as part of an item deal in early October 2019.
Leviathan could be purchased for $4.99 in a limited time deal that included a One Hour Triple Mass Boost. It 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.