Also, I remember a “secret” from World 3 that I used to find in the Japanese version of Super Mario 3 I had when I was a teen- now I have to check my American version if it works as well!

Actually, I knew that since the 1992 exactly, and I always used to do it in that Action Scene 10 in World 6. No news here. I also remember finding a secret “auto select mode” in TMNT3 that same year. Good times.