If you're playing with a less experienced gamer - you know, one of those ones who doesn't know the dash button exists - and they need a bit of help getting over a gap, you can pop a couple of blocks next to each other halfway across the gap and make it easier for them. Alternatively, if you're playing with a cocky chum who reckons he's the greatest Mario player ever sculpted by the gods, you can punish that "swag" by slapping a few blocks in front of their face in mid-air as they jump over a huge gap.
It works for evenly matched partnerships too. Nintendo say that if two experts work together - one with the Wii Remote and one with the GamePad - they can make some pretty "fly, dope and rowdy rowdy" speed runs (our words, not theirs). It's easy to imagine how well this will work, and we look forward to the YouTube onslaught.
Sadly, there just aren't that many opportunities to use the brilliant co-op possibilities - or at least, there weren't in the early version of the game that we played. For the most part during our playtest, the player with the GamePad found themselves just standing there, waiting for the opportunity to place a block.
Fun when you occasionally get something to do, then, but for the most part leaving you feeling pretty powerless. In many situations, the person with the GamePad is going to be getting an extremely short straw, and that's no way for Mario to introduce a new controller to an expectant Nintendo gaming public, is it?
The worst thing is, we know it doesn't have to be this way. Compare New Super Mario Bros U to Rayman Legends, and you can see how Mario's fallen short on the co-op potential of Wii U. In Legends, we've seen huge rotating stages where the player with the GamePad has to turn the whole level 360 degrees so Rayman can get through a mind-messing maze. Compared to this, simply making blocks appear in midair suddenly feels ordinary, and that's something that a Mario game should never be.
Pity the poor sap who gets the GamePad then, but there's no need to feel any such sympathy for the other players, because they get to enjoy a selection of mischievous and game-enhancing new powerups. First and foremost is the Squirrel Suit, which lets Mario glide at a slight angle through the air.
While it might seem obvious that this has taken inspiration from the Squirrel Suit level in Pilotwings Resort, it actually feels closer to an improved version of the cape from Super Mario World. The gliding angle is similar, but while climbing upwards was a struggle in the SNES days - requiring you to dive down then pull back up again - this time you simply flick the controller (or press the ZR button on the GamePad) to zip up again. In practice, it works much like the Propeller Suit did in New Super Mario Bros Wii. (Yes, that again.)