Confession: My favorite Mario game is New Super Mario Bros. for the Wii. It's not the most polished or the most inventive, sure. It doesn't have the most beloved power-ups or the best level design. But it has one thing that has given me more joy than any other feature in a Mario game: multiplayer.
Not just "trade off when someone dies and every once in a while battle in a coin-collecting minigame" multiplayer. Not "Player 2 collects star bits" multiplayer. Not even "there's a separate battle mode and you can run around fighting in it" multiplayer. Real, honest-to-goodness, four-people-struggling-to-make-it-through-every-level multiplayer. And it was glorious.
And the best thing about it was that you could play it more than one way. Sure, you could be nice, with the more experienced players carrying the weaker ones through difficult sections, politely sharing power-ups, using teamwork to get the hard-to-reach star coins. And that's fine! Do that, you'll have a good time.
I'll be busy playing MY way - a brutal race to the finish of every level. Dirty tricks, hoarding of power-ups, intentionally throwing the others into bottomless pits. Nothing's off-limits, as long as one person's alive at the end to grab the flag. And the game's mechanics are perfectly built for this (power-up stealing, picking people up and throwing them, the way the screen scrolls), but without any explicit instructions to do so - the perfect recipe for building your own game mode.
Instead, it quickly became clear to my fellow players that I was using Boost for a different purpose - to turn every level into a maze of suddenly-appearing platforms, erratically moving enemies, and sudden death traps. I would do my best to block jumps, move power-ups out of the way, and basically take on the role of a cruel dungeon master. (I cleared this with my friends, by the way. Mostly. They appreciated the challenge! I choose to believe). The mechanics for Boost Mode are less clearly designed for abuse than the ones in the Wii game, but opportunities are still there. The platforms you can create with a touch of the stylus are the most obvious method of interference, but there are other, more subtle ways to play vengeful God. 3-Up blocks can be revealed by the GamePad player, acting as perfect bait to force players into traps. And a few levels have things like giant gearwheels that respond to the stylus's touch, allowing a savvy bastard to trap and crush his... opponents? Is opponents the right word? in between their gears.
I know, I know. People have been crowing about the 'potential' of the Wii U since it was first announced. But I feel like we're on the periphery of something great, a chance for gamers to interact like never before. New Super Mario Bros. U and Rayman Legends Challenges App are at the cliff's edge of embracing what the Wii U can really do when you trust your players to help you make amazing experiences, and I still have my fingers crossed that, sometime soon, someone is going to take the plunge.