Mashing to 57 is done the same way you mash to 45. Mash enough during the super flash to get the red eye + glow, then keep mashing during the super. Getting the red eye + glow is the hard part, after that you don’t have to go too fast to keep the mashing up. When you’re sure the super has connected, you can always use two hands for the mashing by alternating fingers on certain buttons if you find it easier… that’s what I tend to do.
Basically, pretty mush every mashable super in the game is supposed to add an additional hit on just about every hit, making it 2 hits for every 1 (there are exceptions, usually the first and/or last hit of a super). A super that does 30 hits should become 60 hits, or close to it. What was happening with Haggar’s super however, was that it was only adding the second mashed hit to every other hit… i.e. it was adding 3 hits to every 2. On Haggar’s fully charged RFF there’s a base value of 30, but the first and last two hits don’t get the mashing bonus, so there’s 27 hits in-between. Pre-patch the 27 hits would “only” turn into 42 for a total of 45, but now the 27 mashed hits properly turn into 54 for a total of 57.
I don’t think Ultimate Haggar Buster changed in any way.