I'll settle this. (Well, all the YI arguments, anyway)
The Yoshies on Yoshi's Island? They can swim, but NOT dive. They actually float if you hold them underwater. I think that they can't really siwn that well at all. In SMW, they could KIND of swim with Mario's help (Otherwise, they'd sink.) In YI, they float. Of course, having not really been in the water for a few games, and being on a different island, the Yoshies in SMS cannot siwm at all.
Of course, how Yoshi can swim in the Mario Party games is still a mystery to me...
There IS a Purple Yoshi on Yoshi's Island! It's the one that plays all the x-5 levels. (1-5, 2-5, etc.) There is no Orange Yoshi. I am hoping you are referring to the Brown one that plays the x-6 levels. And there is a Pink Yoshi in SMA3, but not YI. They changed it from Magenta to Pink for some reason. This Yoshi plays the x-2 levels. Maybe it's due to the projection or coloring on your TV?
And if it is, can SOMEONE tell me how to turn any of the Yoshies orange? Please?
Everyone has their own opinions, no matter how WRONG they are.