Super Smash Bros. Brawl/Jigglypuff
In a nutshell
It is 36th on the current Super Smash Bros. Brawl tier list due to several factors. The main such factor is its cripplingly reduced speed from Melee, in addition to its nerfed finishers such as Rest, which instead of KOing under 25% like it did in Melee, it doesn't reliably KO until around 75%, and the reduced hitstun in Brawl, meaning that it can no longer combo as easily as before and making it more difficult to rack up damage. Such factors combine to result in generally poor match-ups in spite of its incredible air mobility and strong edge guarding game.