Some comments on the jiggly matchups from a jiggly main
Ness < Jiggly
This is the matchup I feel like Jiggly is the best at. Ness's best DJC moves of uair and dair are completely outranged by jiggly's nair. Grab also generally works against any attempt to use bair/fair in djc as it like sucks them in. After a grab, comboing ness is ridculously easy (uair, uair, rest and variants). Also, ness can't do too much against dair, which generally means lost stock.
Ness's grab may be really good but it's hard to approach against constant nair.
Lastly, ness's recovery is just easily abused by jiggly who just goes off the edge and easily takes ness out. Not sure if this totally is enough for Jiggly >>Ness though because DJC shield break is a massive pain.
Jiggly= Yoshi
I have trouble understanding why eveyone thinks Jiggly has such a big advantage against Yoshi. There may be very easy combos against a character of Yoshi's weight, but i feel like 90% of the time they're foiled by the second jump of Yoshi.
Then there's shield .breaking DJC, which is a massive threat. Also because yoshi's massive fair hitbox can defeat Jiggly's nair, jiggly has trouble approaching except from above which is risky against Yoshi's usmash.
Edgeguarding Yoshi is also hard for jiggly because she doesn't have a spike, so most of the time Yoshi just absorbs a hit and makes it back.
Oh ya, eggs like own jiggly too because of the massive knockback.
Jiggly < Mario
Mario's fireballs
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Jiggly also has mediocre combos against Mario being unable to combo from forward grab. It's usually just the dair->utilt variety which isn't too bad to DI out of. Fair chains are hard.
Mario on the other hand has dair->uair chains or the dair->grab that is just too good. Mario's dair is also pretty good for edgeguarding the vertically challenged Jiggly.
~ImNotPro