Well before Barbie was in theaters, fans were excited for the Greta Gerwig film, not just because well, it's Barbie, but because of its star-studded cast. The film boasts some major stars like Margot Robbie, Ryan Gosling, Will Ferrell, and Simu Liu, but there are some great cameos as well — including one from John Cena. While fans knew going in that Cena would play a Merman Ken in the film, they couldn't have predicted exactly how Cena's Ken would appear, but now that Barbie is finally in theaters, we know exactly how it all plays out.