Though there are some ancillary new features that take advantage of the Wii U's hardware, the real meat of Tekken Tag Tournament 2: Wii U Edition's console-specific feature set is its "Mushroom Battle" mode, which incorporates power-ups and music from classic Nintendo games into standard Tekken matches. Mega Mushrooms, Poison Mushrooms and other classics litter the floor of a standard match, each performing their expected function when walked on by a character. The results are, predictably, completely hilarious and wacky.
Absorbing mushrooms (or other power-ups like Invincibility Stars) changes the dynamic of the match, as larger characters do more damage and smaller characters move more quickly, for instance. We asked Harada if balance was a consideration while designing Mushroom Battle mode, and he told us that breaking the traditional conventions of Tekken is what makes the mode so entertaining.
At present, it is unknown whether the mode will be online-enabled - in fact, Harada was unable to answer any questions regarding the Wii U's online infrastructure - but we're sure to learn more over the coming months.