It looks as though Amazon.com has slipped up (presumably) with a (presumably) inadvertent leak about Smash Bros for Wii U.
Please see below:
“Take on all comers as Mario, Mega Man, Sonic, and more gaming greats. Or tap an amiibo to the Wii U GamePad controller to train it up by battling with or against it. You can even pit your amiibo against a friends’ to see how your training methods stack up. Whether you’re creating stages on the GamePad, competing in challenges crafted by Master Hand and Crazy Hand, or outwitting your opponents in a brand new board game mode, there’s no doubt that the ultimate Smash Bros. game has arrived.”
Think of the possibilities! But this all comes in the wake of a recent word from Sakurai that there is much content unique to the Wii U version of Smash Bros that 3DS won’t have; so-much-so that he entertained the possibility of a Nintendo Direct possibly coming up soon… until then, it’s all just speculation 
Thanks for reading,
-Kendo