Rabid is one of the four skins released under the Party part of the Agar.io Birthday offer. It was available for purchase in late July 2017.
Rabid could be purchased for $9.99 as part of the Birthday Pack. This pack also included the Delighted skin and either 7000 coins and a Mass Boost (3X, 24H) on Browser or 1800 DNA and a Birthday Potion on Mobile. Rabid was not available for individual purchase and may not be available for purchase in the future.
Details of this offer may vary depending on location and platform.