Thanks for pointing that out! I tried looking for it, but couldn’t find it — would you mind letting me know where exactly it is and how to get there?
Viewing post in Mirage Castle DEMO3: Exploring Platforming Mechanics comments
its just after the checkpoint in the very top right of the level - you drop down onto a diagonal moving platform (that has the blue triggers on it )
if you then jump off to the left you fall through a piece of black background and disappear off the bottom of the screen ... i found it when searching for coins !