Thirteen new Mario based sets are available on K`Nex website.
Sets parts are vert specific. Experienced MOCers will find a way to use such bricks, but i won't recommend to buy this sets for building. This is more from a toy, than from a construction toy.
This sets are very colorful, and will be great for playing with them. Mostly new sets are consists of cars and tracks for them.
As it was said in press-release, we had got Bowser minifigure, it could be found only in two sets, so no it has replaced Yoshi's place of the rarest minifigure in the series.
This is the reason why K`Nex 38436 is so interesting, if you buy it you will get two rarest minifigures in the series: Bowser and Yoshi. As you may remember, press-release also told us about a Princess Peach, so i think we will see more new sets soon.
To see sets information together with some promo videos you should go to K'Nex Mario Kart Wii section.