New Super Mario Bros. U
New Super Mario Bros. U
The game was developed long before the Wii U even started development. In an Iwata Asks interview, Masataka Takemoto stated that the team used materials from New Super Mario Bros. Wii. By the time the Wii U GamePad was announced, he considered having four-player cooperative play with an extra player using said GamePad to add blocks.
Contributed by GamerBen144
The developers tried using Mii characters in the story mode, but thought that it no longer felt like a Super Mario game, so they created other game modes where the player can use their Mii characters.
Contributed by CuriousUserX90
In a mini boss level, if you defeat the enemy and wait about 30 seconds, Nabbit will appear, steal your prize and then jump off screen.
Contributed by Boyobmas
On the second loop of the title screen, Luigi won't jump and ground pound with the rest and will look confused, briefly, before turning to run as usual.
Contributed by Boyobmas
New Super Mario Bros. U began as a tech demo, shown at E3 2011, called New Super Mario Bros. Mii. It allowed players to use Miis in all modes. If all four players chose Miis, Player 1 would be dressed as Mario, Player 2 as Luigi, Player 3 as Wario, and Player 4 as Waluigi but with blue sleeves.

While Miis are no longer selectable in all game modes, this concept did make it to the final game in the form of "Boost Rush Mode".