Hydra Dragon is one of the three skins released under the Noble Pack part of the House of Dragons offer. It could be individually purchased with game coins in late September 2017.
Hydra Dragon could be purchased in the Skins Shop under the ‘House of Dragons’ tab for 1900 coins. This skin was available for a limited time and may not be available for purchase in the future.
Details of this skin can vary depending on location, platform or time.
Note: The Noble Pack sub-offer was released again for a limited time in late May 2019. The price for Hydra Dragon remained the same at 1900 coins.