Storm Fist is one of the three skins released as part of the Action Heroes (Volume 1) offer. It could be purchased as part of an item deal in late April to early May 2017.
Storm Fist could be purchased for $9.99 in a limited time deal that included 16000 coins. 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 first volume of the Action Heroes offer was released again for a limited time in late January 2019. The price for Storm Fist and the 16000 coins was lowered to $4.99 for this release.