With OMGT3, I wanted to communicate the idea that Juni is living in a drug-fuelled fantasy land. The grey rooms represent the reality Juni sees when the drugs have worn off. I think I must have been subconsciously inspired by yohji's level
Silver Lining, since that does almost the exact same thing, but communicates it better.
The generic quest set-up is meant to suggest that all Knytt Stories levels might just be Juni's drug-induced delusions. However, I never found time to emphasise this idea due to excessive time spent implementing that 'interactive' pill scene, which turned out to be a bit underwhelming anyway.
The ending sound effect is achieved simply by setting a brief Music file to play during the Ending cutscene in World.INI, then deleting the Ending folder.