Hey, so in my testing I've been labbing a bit with this:
https://m.youtube.com/watch?v=bEVDvfzcvXU
Not the shield break (I am thinking about a version for us, but that's not what I need help with), but the combo. Specifically, the second one. What he does, is z-drop, fastfall, item hits them, footstool, z-catch, wait, z-drop, fastfall, item hits them, footstool, z-catch, and repeat. When the jump eventually gets too small he goes to the side and then shorthops back, with a z-drop to footstool, z-catch, then repeats the whole combo. I don't think the hydrant is necessary at all, as he demonstrates.
Basically, I'm trying to get this to work for bayo. She seems to have the perfect jump height and fall speed to be able to do this. But I'm having trouble doing it with either her or pac-man. The best way to lab it I've found, is vs Mario in training mode, 1/4x speed, 999%, using star rods(bouncy items that behave just like pac-man's items), and then before the combo footstool Mario to get perfect positioning. These combos wouldn't only annihilate pac-man in our MU with him, but would also be possible and practically identical with any other bouncy non-explosive item(peach'es turnips and items, sheik's grenades, robin's tomes and sword, rob's gyro, any of pac-man's items, and villager's wood chip), and could be ended with a dair for the kill.
So the problem with I'm having, is with both pac-man and bayo, I get as far as z-drop, item hits, footstool, but then I either z-drop too late and Mario stands up first during invincibility frames, or I z-drop too early and he gets launched before I can fastfall and get the footstool. So it's a tight window, but it feels slightly easier for bayo. I just wanted to see if any of you guys could get it, and also to share it with you, it's sort of like wobbling, a strict input timing infinite combo, and I think it may eventually be a staple in top level play, after all, some random player in Japan was able to do it consistently so top players should be able to too. Also, I don't think it requires a shield break to start, shorthop z-drops really aren't hard to land in the neutral or as a punish, and are extremely safe. Also if I find some good shield breaker combos with items they're gonna be way too scared to shield them.