- initial idea was to expand upon “secondary play” by adding a bunch of Boost Rush courses
- this idea was transferred to New Super Mario Bros. 2
- the “U” team was quicker to come up with DLC ideas than the 2 team
- the team developing “2” came up with the idea for Coin Rush courses as DLC

“We originally assumed the downloadable content would be for people who had played New Super Mario Bros. U, and decided to make it for people who wanted to play it even more. So I had been saying it could be a little more difficult.” - Tezuka

- stages were shortened to deal with the more difficult design
- this was partly inspired by Super Mario Bros. 3
- team members from the New Super Mario Bros. 2 team were brought over to help out
- the game originally had Mario in it
- this changed once Tezuka heard about Nintendo’s “Year of Luigi” plan
- Luigi's abilities helped balance the game as well
- each tick on the clock was made slightly longer than in New Super Mario Bros. U
- sales teams around the world requested a retail version for those that didn't have NSMBU