Gentlemen and ladies, I would like to submit this thing which I haven't seen exhibited on the site, and which most definitely is a game glitch.
http://www.youtube.com/watch?v=bpoV5imBbZw
The stage starts at 3:38, and the payoff is at 5:17. I don't know the precise process here, but there's something with the bubbles and the Yoshi falling in that pit. There's at least one other example of this trick being done by these guys on this user's channel, so I suppose it's not very difficult, but the effect is distinctive and amusing. It's not really my place to make a request, but if this glitch were explored and understood and exhibited in later runs, I would just be super jazzed.
On for this run, I dig it a lot. I've seen a lot of tricks and glitches in SMW since I started watching videos here, and there were still a good number of jawdrops to be had. I applaud!