Smash Bros. released with a handful of bugs. Personally, I don't think they're bad. They're features. Funny features! (Well, unless they get annoying and screw up gameplay.) The latest bug, it seems, is turning Yoshi into Giant Yoshi. Or better yet, GODZILLA YOSHI.
As seen on Twitter and YouTube (via Otaku News), the bug seems to pop up during a mode in which players take on a handful of CPU enemies. If you play as Yoshi and keep laying eggs, it makes enemies bigger and bigger, until your opponent takes up a huge chunk of the screen and then pretty much smushes you.
Your opponent doesn't have to be Yoshi, it seems.
Yikes! Thankfully, this doesn't seem to affect versus play and is confined only to this mode.
In case you missed it, check out Kotaku's round-up of Super Smash Bros. glitches.