I was reading the Tips in HD Remix when they brought this up. What exactly is it, how do you use it, and is this the reason why people mash buttons after using a Finisher in MvC2?
it’s something that gives you more opportunities to land reversals
ex: inputting something like f, d, df (hitting all three punches, then releasing) gives you 6 opportunities to reversal dragon punch
or something like that, i’m sure i explained it like ass
When you are recovering from a fall, and your opponent is pressuring you (Waiting to attack/cross up as you’re recovering) you’ll basically want to reversal any special that will get you out of a bind, such as a Shoryuken with Ryu or Ken.
The window of timing to input the command (forward, down, downforward + punch) is fairly strict. Now, if you want a higher chance of pulling off that reversal, you’ll want to try and get more than just one “punch” inputted to make up for difficult timing. So, when waking up, you: input the control motion (forward, down, downforward + punch), then in succession push down light punch, medium, heavy (Or vice versa, heavy punch - light), and then in SUCCESSION again release the keys.
When you push down the keys in succession, you’re basically pushing punch 3 times in quick fashion. So, when you’re doing this, you have a higher chance of pulling off the reversal…now the cool part is, when pulling off specials, pulling OFF the button (as in, pulling your finger off of the punch button) counts just as much as pushing it (Again this only works with specials. If you push down the punch button, and then release, you won’t punch on release, but can release the punch button when doing something like hadouken or shoryuken).
So in reality, the game is reading 6 quick successive inputs of “punch” giving you a much higher chance of timing it with your motion correctly, and thus pulling off the reversal.
…That was longer than I expected, and seems a little confusing. If anyone can shorter my paragraph and make it more legible, be my guest 
Hope that helps!
the piano meathod has definately helped me with learning wakeup and reverals specials… its worth learning and very easy, even if you play on a pad. You don’t need to input the buttons perfectly or anything, just kinda roll your thumb and fingers, or your fingers if playing on a stick. It’s especially useful for characters that it doesn’t really matter if you get different versions of the special to come out.
[media=youtube]t8dD3K2_Pz4[/media]
1:00
i dont think this has anything to do with mvc2, AFAIK the only reason to mash is to get better damage on the ahvb or the hailstorm.
Some people “mash” the buttons to get the super out, seeing as though the piano method works for getting your super out