All Doc has against Jiggs over Mario is random F-airs out of grabs at the right percents. Getting grabs against Jiggs honestly is also pretty random, as is landing most ground moves not named F-tilt and U-tilt in this matchup. For the most part I really don't think the matchup for Mario and Doc vs Jiggs is really any different.
The only two matchups high tierish matchups where Doc I think is noticeably better are against Sheik and Ganon, who both Mario and Doc can kinda easily get in on on the ground, but Doc clearly likes having a better D-smash and F-air when he needs kills.
Actually I almost forgot. He's probably better against Samus too. But against Spacies, Peach, Jiggs, Marth, and the ICs, I'd consider it mostly down to preference. And against Falcon, Mario is definitely better.