Most viable characters have the necessary tools to have a slight or significant advantage against Jigglypuff, but Jiggs has the ability to "cheese" stocks while being very resistant to similar "gimmicks" from other characters. This means that maintaining the advantages that win you the matchup requires a lot of executional finesse - which is incredibly difficult to maintain throughout a tournament set. Hungrybox's talent comes from his ability to stay even or near even with the top players of Puff's worst matchups, and then immediately and consistently capitalize off of any execution or positional mistake with a kill.
Marth is definitely favored against her, but there aren't any Marths near Hbox's level right now. PPMD isn't playing (and actually has not met Hbox in bracket in recent memory), and M2K is in a slump - not to mention his Marth is notoriously bad with floaty matchups at the best of times (he'll most often opt to go Fox). PPU took a set at Apex 2015, but Hbox has certainly leveled up since then while PPU hasn't shown that level of play for quite a while.
Sheik spends most of the game vs. Puff in favorable situations, but for her the matchup is a game of severe attrition, which while she will generally win, makes any stocks lost to a rest incredibly hard to come back from (she also has problems punishing rest, meaning Puff isn't as scared to go for it as she is against Fox). Combined with Hungrybox's particular strength in the Sheik matchup and superb ability to capitalize on mistakes as well as his immense stamina, makes him a very difficult opponent for Sheiks, especially in longer sets. That said, players like Plup and Swedish Delight have ocassionally shown the ability to stand toe-to-toe and come out ahead against 2016 Hungrybox for several stocks or even games, and if they could maintain that level of play over a longer period of time they could definitely take a set.
Falco's toolkit is arguably the best out of all three of these characters for dealing with Jiggs, but conversely is punished by far the hardest for even the slightest of mistakes. It's incredibly difficult to put a number on this matchup, because while if neither player makes any mistakes Falco should never be touched by Jiggs, in real-time tournament play beating a Hungrybox level Jiggs with Falco requires a level of precision that is ridiculously difficult to maintain over the course of a set. Similarly to Marth, there's also a talent issue - there are few strong Falco's in the world, and while the Falco-jiggs matchup is favorable in theory, Mango is much better off relying on his Fox, which before 2015 was nearly undefeated versus Hungrybox, PPMD doesn't show up to much and hasn't played Hbox since Evo (and in the future may opt for the more consistent Marth matchup). That leaves only Westballz, who took a set from Hbox at MVG Sandstorm - there was some setup-switching jankiness involved, but even discounting he is constantly called by the (in my opinion, incorrect) urge to play his Fox in the matchup, and Hungrybox's drastic improvements in placings and consistency since then is only mirrored by Westballz's drastic atrophy in the same area - making it a very weak prediction that we'd be able see his Falco contend with Hungrybox.
The only other matchup that Jiggs arguably loses to is Falcon, which has a similar talent problem to Marth and Falco - however, the Florida 20GX crew's constant access to the matchup is promising, especially as they all continue to improve as players in general.
Tl;dr: Jiggs arguably loses to Falco, Marth, Sheik, and Falcon, but none of these characters have the combination of available talent and consistency to threaten a Puff of Hbox's caliber.