Delli is one of the three skins released in The Sugarrush Planet event. It could be purchased in the item deal part of that event in mid October 2020.
Delli could be purchased for $9.99 in a limited time deal which included a package of 25000 coins, 1500 DNA and 3000 lollipops. 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.