Tip: Make sure that ALL exit-enabled pipes, doors, etc. have a screen exit defined, or they'll take you to Level 0, the "endless" bonus game. Unless Start+Select is enabled, the only way out of it is to reset the game.
Dude, I can't believe that. I was looking exactly something like this today in the morning. Didn't find anything. Then I searched on google now and found this. Almost some hours later this was accepted: exactly when I was about to give up trying to find something to fix this annoying enemy. So, imagine you are trying to fix something and few hours later the exactly thing you wanted is accepted. I never saw a coincidence like this in my life. Thank you so much! I will test to see how it works.