Best of Agar.io is a special offer that contained a set of previously released skins. These skins could be purchased individually in the Skins Shop under the “Best of” tab. These skins may not be available for purchase in the future.
The skins in the first edition of 'Best of Agar.io' offer were available for purchase in early December 2017. They included the following four skins: Walrus Ball, Dumpling, Bubblesaurus and Black Beard.