There is a change that the drivers can change looks, at least PEach with clothes. She uses a dress in cars, but look: she uses tight sitting clothes when biking. I haven't noticed this on any other characters though. 
Koopa Troopa is definate: 
Ok, for a time here, we were going faster than the Brawl thread, but now it is going faster than us!
How much do you hype MKWii? Range: 1-200 Brawl is 100. I have to go at 113 I think.
The badass Mario Car is real. Upper left, I doubt they would do that multiple times-. 
Edit: More tournaments confirmed? The two first are Mushroom Cup and Flower Cup. The next are almost certainly Star Cup and Special Cup. Then comes a shell and a banana - I don't know what those are. This also pretty much confirmes mirror mode, as there are 4 downwoards. 
Whoa, intreresting fact about snaking. In earlier games, you remember that the spark first turned blue, then orange, right? In all the power boost pictures I've seen so far, there have only been blue sparks. No orange ones. Perhaps this means snaking is sort of gone, and that only the boost itself is gone? That it is now only a quick way to get past corners. Let's hope so.
http://www.vgchartz.com/games/userreviewdisp.php?id=261
That is VGChartz LONGEST review. And it's NOT Cute Kitten DS
