Stretch Dog is one of the three skins released in the Doggos of Agar.io offer. It could be purchased individually using game coins in mid February 2020.
Stretch Dog could be purchased in the Skins Shop under the ‘Doggos’ tab for 3200 coins. This skin was available for a limited time and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.