This is actually a secret. This shell only appears if you have a fortune of 80 or higher. So for most people it's not there.
And for the other bugs, fixed all of them now.
Thanks^^
It's accecible in normal game as well, I only have hidden the red switch in version 1.0. Before it was in the demo end area. Now this switch is hidden somewhere in the world, making that secret even more impossible to find.