I'd say the only major change in Jigglypuff that wasn't a nerf in Brawl was probably it's Rollout attack.
Rest was nerfed. She also became much more frail. If you don't believe me, the official tier list shows a huge drop from melee to brawl. I know a lot of you are iffy on tier lists, but I find them to be reliable in terms of ranking characters. The Smash wiki often elaborates on the reasoning for a character's tiering, and the constant revisions and statistics behind their tiering makes it seem quite credible, at least to me.


pardon my stuffty screenshotting but i think it gets my point across
Also, low tier characters DO have strengths over high-tier characters at times. There are a lot of great low-tier players out there, like this one famous Lucas player that I don't know the name of (I'm not very active in the Smash community).