So I'm flitting between work and school and more, but I thought I'd post this...

Last night I was dashing about the Good Egg Galaxy, and I thought I'd explore the innards of the house in the first clearing.  Once in the cellar, I proceeded to  approach a small ramp which normally lets one walk up the wall, but somehow found myself falling through the back of the wall and into the "murky swirling blackness in the background" effect instead.  I appear to have managed to sneak between polygons and get myself stuck.  Interestingly, Mario didn't die, he just sort of vanished into the black, swirling stuff.

I haven't been able to repeat this yet, so I'm not sure if it's pure happenstance or a particular entry angle.