Mario & Luigi: Dream Team spent three years in development because studio AlphaDream chose to render the characters in 2D pixel art and shade them to look 3D, while all backgrounds were initially created in 3D, according to the latest Iwata Asks feature.
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.
Backgrounds were made from the start in 3D, but making 2D pixel art characters look three-dimensional and rendering their animations was difficult to create for the Nintendo 3DS stereoscopic capabilities. The larger the on-screen character, the more readily apparent the 2D rendering became. The art team went through many iterations of scenes using larger figures, such as boss battles.
"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. In instances where multiple Luigis appear and clump together, each one is positioned differently and moves in a slightly different way — details that took an enormous amount of effort, since no pre-existing data was used.
Read the full Iwata Asks interview here.