The Hatter is one of the two skins released in the second volume of the Easter Wonder Fest offer. It could be purchased as part of an item deal in early April 2020.
The Hatter could be purchased for $9.99 in a limited time deal which included a package of 3500 DNA and an Legendary Potion. 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.