To be fair jiggs was never meant to be a serious character. That said I still want her down air to break shields if all the hits connect.
That's not really a good excuse. There are people out there who actually like the character and are rather unhappy with the state she's been in for the past two games.
So I guess I'll propose some changes as well.
Forward tilt - BKB increased: 8 -> 16
Up tilt - KBG decreased: 120 -> 90, hitbox size increased.
Up smash - active frames changed: 16-19 -> 13-16. Upper body invincibility on frames 13 - 16. FAF: 46 -> 31.
Down smash - damage increased: 11% -> 14%, startup decreased by 3 frames: frame 14 -> frame 11.
Back air - hitbox active: 12-13 -> 8-9.
Down air - landing lag: 30 - 15, final hit now meteor smashes aerial opponents weakly.
Up air - startup decreased: frame 9 -> frame 7, landing lag decreased: 15 -> 10.
Forward throw - angle lowered to semi-spike trajectory.
Down throw - damage decreased: 4%, 6% -> 3%, 4%. Knockback: 45 base, 100 growth -> 40 base, 80 growth.
Back throw - angle lowered.
Up throw - knockback: 30 base, 110 growth -> 70 base, 120 growth.
Rollout: No longer causes helplessness after connecting.
Pound: FAF: 46 -> 40.
Rest: Forces Star KO.
Sing: I don't even know how to fix this move.
Here's some buffs of Puff that should happen:
Weight Increased: 68 => 73
Air Speed Increased: 1.269 => 1.4
Fall Speed Increased: 0.98 => 1.3
Fast Fall Speed Increased: 1.568 => 1.934
Down Tilt Hitbox Active: 10-12 => 7-10
Down Tilt FAF Decreased: 30 => 26
Forward Smash Hitbox Active: 16-19 => 13-16
Forward Smash FAF Decreased: 50 => 38
Up Smash Hitbox Active: 16-19 => 13-16
Up Smash FAF Decreased: 46 => 29
Down Smash FAF Decreased: 49 => 39
Forward Throw KBG Decreased: 100 => 30
Forward Throw Angle Changed: 55 => 70
Up Throw KBG Increased: 110 => 150
Down Throw KBG Decreased: 100 => 40
Back Aerial Hitbox Active: 12-13 => 8-9
Down Aerial Damage Output Increased: 1.5% => 3%
Down Aerial Last Hit Damage Increased: 2% => 4%
Pound FAF Decreased: 46 => 32
Pound Shield Damage Increased to +25%
Rest FAF Decreased: 230 => 210
Rest Shield Damage Increased to +30%
Rest Angle Changed: 88 => 50
Now Rest and Pound are REALLY dangerous on shields since if you don't Perfect Shield, Pound will make your shield go down quite a lot, but Rest will instantaneously break the shield. As well, mobility and frame data increase will aid Puff's ability.
Your changes are pretty good (I had to steal a few of them for myself), but keep in mind that Jigglypuff is, first and foremost, a balloon. It'd go against her design (even though a ****ing outline shouldn't weigh more than a balloon) to buff her weight and increase her falling speed. Especially by such a wide margin, that would end up hurting her, I think.