Young Bonny is one of the three skins released in Pirate Planet event. It could be purchased in the item deal part of that event in early December 2020.
Young Bonny could be purchased for $7.99 in a limited time deal which included a package of 1400 DNA and 1500 gems. 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.