Infernus is one of the three skins released under the Dark Dimension Zone offer. It could be purchased individually using game coins in early March 2018.
Infernus could be purchased in the Skins Shop under the 'Dark Zone' tab for 690 coins. This skin was available for a limited time and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.
Note: The Dark Dimension Zone offer with the Infernus skin was released again for limited times in late June 2019 and then in early November 2020. The cost for Infernus remained at 690 coins for each release.