The First Birthday sale is a set of six skins that were released to celebrate the first anniversary of Agar.io in 2016. Each of the two parts of this offer included different skins. These skins are no longer available for purchase.
First Birthday (Shop)
These 5 skins are only able to be bought using game coins. They became available for a limited time in the Skin Shop under the "Birthday" tab.
The First Birthday skins in the shop are as follows: Birthday Sanik, Birthday Wojak, Birthday Cia, Birthday Sir, and Birthday Doge.
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First Birthday (Money)
The two skins in this part of the offer could only be purchased using money with various packages of coins. The skins were not available for individual purchase.
The First Birthday skins included the following: LOL and Birthday Troll.
An image of the "First Birthday!" offer.
There are little to no info on this sale, so this article is not very detailed.