Bitter is one of the five skins released under the Skins part of the Agar.io Birthday offer. It was available for individual purchase in mid July 2017.
Bitter could be purchased in the Skins Shop under the ‘Birthday Special’ tab for 3320 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: Bitter was released again for a limited time as part of the All the Internet Things offer in mid November 2019. This time the price for Bitter was increased to 3900 coins.