In a conversation with Nintendo boss Satoru Iwata, the development team for Dream Team said it took around a year and a half to build the alpha version of the game off the original prototype, and another year an a half to create the beta version and eventually a third gamma version.
"We worked out special ways of drawing and using color to make them look three-dimensional," said Nintendo producer Akira Otani. "The work load was tremendous, but thanks to that, it has the sort of smooth polish distinctive of AlphaDream."
AlphaDream had to render animations for Mario and Luigi moving in 16 different, distinct directions. The studio couldn't simply mirror the data for each movement, which the team explained was because Luigi has an "L" on his hat and Mario raises his left arm when he jumps — both movements that can't be mirrored and kept identical.
http://www.polygon.com/2013/7/3/448...am-three-year-development-due-to-2d-pixel-art