It's called the Midnight Mint Mocha Frappuccino and supposedly, it tastes like a Thin Mint Girl Scout cookie!
The layered beverage is made with scoops of extra-dark cocoa that's blended with coffee, milk, and ice. The drink is also infused with cooling mint sugar ~crystals~ and a layer of whipped cream, then topped with even more whipped cream and an additional dusting of dark cocoa. [Source]
Unicorn Frappuccino who?