 Several celebrities made live action cameo appearances on the film, including Rosario Dawson, LeBron James, Tina Fey, Will Ferrell, Craig Ferguson, Robin Williams and P!nk, while Ricky Gervais provided opening and closing narration for the film.Animation was handled overseas in South Korea at Rough Draft Studios.Animation directors credited with episodes in the sixth season included Andrew Overtoom, Alan Smart, and Tom Yasumi.