1. choose falco
2. start doing pivot grabs with normal grab button, but make sure you dont run too much, like run a LITTLE bit and quickly pivot grab.
you should notice that falco doesnt move at all, hell just stop, turn and grab.
3. now do the same thing, but with R+A (or, L+A, whatever). make sure to not run very much.
you should now notice that falco gets a major boost. theres only one explanation- boost pivot grab.
another test if you still dont believe me is attempting to boost pivot grab your "normal" way with meta knight. MK doesnt get very much boost, if any at all, but usually if you do the boost pivot grab correctly, youll hear him make a noise, which he doesnt do if you pivot grab normally.
now try to to pivot grab with R+A, you should hear that noise.
now, like i said before, it wont come out EVERY time, you have to get the timing down. but it does work.