Hades is one of the three skins released under the Heavens of Olympus part of the Olympus offer. It could be purchased as part of an item deal for a limited time in early September 2017.
Hades could be purchased for $4.99 in a deal that included 3250 coins. It could also be purchased for $19.99 in a the "Best Deal!" which included the Zeus skin and either 50000 coins (Browser) or 1800 DNA (Mobile). It was not available for individual purchase and may not be available for purchase in the future.
Details of this offer can vary depending on location, platform or time.
Note: The Heavens of Olympus sub-offer was released again for a limited time in early October 2019. The deal that included Hades and a package of coins remained at $4.99. However, the included coins were increased to 5000. The Best Deal was lowered to $14.99 on browser and stayed at $19.99 on mobile. A package of 1200 DNA was included on both platforms this time.