Tip: Layer 3 backgrounds and tides disappear when you hit a message box, so plan your level around that. For example, you can add a sublevel without layer 3 at the start/midpoint, and include your message there.
Are you going to make any patches? There is a really annoying invisible wall in Course 9: Magma Mountains. It's on the bridge that leads to the Lava Spire Star. You have to jump on the right-most side of the bridge to get past it. A very fun game otherwise, can't find the Wing Cap though... :/