I just noticed something about the being pushed off a platform thing.
when I play sans ike I sometimes try to do this, and push him off a platform. usually when I do this he instantly back airs me.
I think that if you get pushed off a platform and your FACING the end of the platform you were on, you can react instantly, but if your back is to the edge and you get pushed off, it puts you in some kind of weird rapeable hitstun.
Kind of like in real life, if you trip facing forward you see where you are going and can thus regain your balence, but if you fall backwards into a gap, youre more likely for injury because you cant really react to falling backwards, if that makes sence.