Flying Saucer is one of the three skins released under the Dark Dimension Zone offer. It could be purchased individually using game coins in early March 2018.
Flying Saucer could be purchased in the Skins Shop under the 'Dark Zone' tab for 490 coins. This skin was available for a limited time and may not be available for purchase in the future.
Details of this skin may vary depending on location, platform or time.
Note: The Dark Dimension Zone offer with the Flying Saucer skin was released again for limited times in late June 2019 and then in early November 2020. The cost for Flying Saucer remained at 490 coins for each release.