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.
New: This is a small update that should fix the glitch where Yoshi doesn't always disappear in a puff of smoke and makes it so baby Yoshi can't pass this block either.
Old: A block that if riding Yoshi forces the A button to be pressed forcing Mario off of Yoshi, Yoshi then dies in a puff of smoke and plays a sound. Sound is easily changeable.
Tester's note: It still doesn't always kill the Yoshi. Try entering the block from the bottom.