So, I have an interesting theoretical question for you.
http://www.youtube.com/watch?v=YdSOLalEs7Q&feature=related
Doing this with debug allows the Marble Garden 2 boss to appear in
Hydrocity 1, and when you complete the boss the game sends you straight to Carnival Night! The video isn't overly descriptive about how you get to the position where it starts, but basically you have to die in the first area, activate debug and go across to the area in the video.
What I'm most curious about, is obviously, why the hell does the boss appear, and secondly can it be done elsewhere, or with other bosses? Interestingly there are at least two related videos that show the Carnival Night 1 miniboss appearing in interesting places... though that isn't as useful.
Also, when I tried this on my console, when I tried to pass below the water level I crashed my game. Is there anything in the emulation that would explain this?