I know I've already posted a request, but I just noticed something weird..
In the Loop-De-Swoop Galaxy (the second Manta surfing course, part of the Trial Galaxies), there is a platfrom that has sling star and a giant ?-Coin (I guess that's hwat you call it. The same kind of coin that triggers the Bee Shroom in the Beebee Kingdom) As you are surfing through the course, it is just after the second 1up in the course, a ways behind those panels that have Star Bits attached to them.
As of yet, I have found no way to get across the giant gap on the Manta, but after you finish the course, you can do a spin jump off the coach's head, and if you are pressing toward the front gate of the course, you might be able to land on one of the points on the star gate, thus enabling you to swim the course without the Manta.
I've explored the course before, but never noticed those platforms and sling star until last night. Has anybody else found out why they are there?