Big Banjo is one of the three skins released in the multi-part Mino's Christmas Special offer. It could be purchased as part of an item deal in late December 2018.
Big Banjo could be purchased for $9.99 in a limited time deal that included 25000 coins, 1200 DNA, Dasher and Snowy Joe. This skin was not available for individual purchase and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.
Notes: Big Banjo was released again for a limited time under the Cats of Agar.io offer in early March 2020. This time Big Banjo could be individually purchased for 4200 coins