So I was playing against my friend today and he was using jigglypuff and I was using captain falcon. He used sing and I was going to falcon punch him but instead of the falcon punch hitting jigglypuff, captain falcon slid across the screen. I tried replicating this by myself and I was able to do it with warlock punch and falcon punch. I haven't tried it with any other attacks.I'm pretty sure in order for this to occur the falcon/warlock punch has to be far enough away so that it almost hits jiggly.

Sorry if this has already been discussed as I don't know much about jiggly and couldn't find it on these forums. I dont know if it could have many uses but I thought I would share it.

Funny, I did something similar today as well...
Cool coinky-dink. Looks like we have a character specific mindgame? Lol.

good find. I'll look into it.

http://www.youtube.com/watch?v=Bmy5zEu1edc&feature=related

Video of it, not made by me.

It's a weird Falcon Glitch. Falcon Punch will slide along the screen out of certain moves. I know that Vanish (Sheik's upB), Mario's Cape, and I think Pit's shield will do this, but I don't know all of them. Looks like this is just another one of them... lol.

It isn't just Falcon, it's been done with Wolf and Falco as well. It's something to do with Jiggly's Sing.

The thing that could make it useful is that they are sleeping when they come out of it. So at higher percents it might be able to be used to set up for a kill. The timing would have to be really precise though.

I believe this has been done with Yoshi (lol) too but I don't have the video on me atm. Weird stuff.

Hmmm... it appears to have a "wind" effect" similar to Pit's UpB or Shieks Vanish.

Ah, here's what I was talking about: http://jp.youtube.com/watch?v=LBAb9qdxMcY

Sorry for youtube being in Japanese region, but my friend was in Japan when he sent it to me (and I'm too lazy to set it back to English)

I noticed in the video that fox,yoshi, and falco were about to shield the attack so it can be trigured that way. But it doesn't explain falcon punch. This my be useful.

http://www.youtube.com/watch?v=rOlNKLqaxBg&feature=related

Here's a video I found of it with wolf. This could be useful if you do it near a ledge since the opponent stops sliding when it gets to a ledge so if you're near the opponent you could attack them.

with this slide could you use it to make someone go to sleep and they slide off the ledge asleep still making them unable to recover

No, when I've done it they stop when they hit the ledge unfortunately,

It's not just her sing something is probably wrong with the games mechanics or something.
This is something that should really be looked in to.

Looks like the sleep cancels the animation of the attack/roll causing the sliding part of the animation to continue. Pretty neat but I don't think it'd be useful for anything.

It happens when the hitbox of Sing comes in contact with movement increasing frames of a move. (Rolls, apparently Falcon Punch) Jayce is pretty much right.