Sea Turtle is one of the five skins released under the Mystery Island part of the Island offer. It could be individually purchased with game coins in September 2016.
Sea Turtle could be purchased in the Skins Shop under the ‘Mystery Island’ tab for 690 coins. This skin was available for a limited time and may not be available for purchase in the future.
Details of this skin can vary depending on location, platform or time.
Note: The Mystery Island sub-offer was released again for a limited time in early April 2019. The price for Sea Turtle remained the same at 690 coins.