Berserker is one of the four skins released under the Winter Warriors offer. It could be individually purchased with game coins in December 2016.
Berserker could be purchased in the Skins Shop under the ‘Winter Warriors’ tab for 4900 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 Winter Warriors offer was released again for limited times in mid April 2019 and then in mid December 2019. The price for Berserker remained at 4900 coins for each release.