Monkey is one of the two skins released in the Treasure Hunt part of the Pirates offer. It could be purchased as part of an item deal for a limited time in August 2016.
Monkey could be purchased for $19.99 in the "Best Deal!" which included 50000 coins. This skin 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.
Note: The Treasure Hunt sub-offer was released again for a limited time in early May 2019. This time the price for Monkey and the 50000 coins was lowered to $9.99.