No special items, which is kind of a shame as there is no difference between the weight classes other than how they look (Everyone in each weight class can use the same bikes/karts too). Still, at least we now see the death of the Bowser shell.
Yeah, Rosalina has a Luma riding with her, although it's kind of hard to tell whether it's the same one in Mario Galaxy (it probably is though). She keeps the same weird-cool voice which is pretty much the reason why I use her ;D
For those of you who are wondering what the difference between Karts and Bikes are, the karts can get a much larger boost with drifting if you hold it down long enough, while the bikes can perform wheelies at any given time to make you go a little faster. They are pretty balanced, neither outclassing the other, but if you use the wheel that comes with the game then sticking with the kart is... good advice. I would say Bikes are also harder to control overall, but best for time trials- that's just me though, I have seen some truly incredible players using the Kart.
Oh yeah, stunts. These aren't nearly as gimmicky as one would expect, because it requires a certain amount of thought to successfully pull one off. Simply doing a stunt is easy; simply flick the remote whenever you go up a ramp, and when you land, you get a speed boost. But as all you veterans know, the speed boost isn't always a good thing... [/rainbow road]
I could talk all day so if you have questions then just ask ;f