Mushroom Bot is one of the three skins released in The Fungus Amongus Planet event. It could be purchased in the item deal part of that event in late May 2020.
Mushroom Bot could be purchased for $7.99 in a limited time deal which included packages of 3000 mushrooms, 12000 coins and 6000 DNA. It 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.