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When game data is transferred from the Wii to the Wii U, an animation will be shown of the icons of the transferred games being carried by Pikmin, creatures from the Pikmin series by Nintendo.
Contributed by yoko19191
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The Wii U Gamepad Prototype was just two Wii Remotes and Nunchuck analogue sticks attached to the sides of an LCD screen.

They also created a prototype for the Wii U Zapper which consisted of an LCD screen attached to a Wii Zapper.
Contributed by pkmngmr
In a previous Iwata Asks Interview from 2011, Satoru Iwata stated that the Wii U hardware started development back in 2008. This means it started development 2 years after the original Wii was released, 3 years before it's debut at E3 2011, and 4 years before it's release.
Contributed by pkmngmr
The Wii U Mii Maker's music contains the music used for the Great Fairy Fountain in the Zelda series, and Super Mario Bros 3's Water Land.
Contributed by Skarro
If you enter the Wii U's menu on your birthday, special music will play and all of the Miis will clap for you.
Contributed by RayMonkay