Okay, ROB's nair is so **** annoying. But I find that fairs are so effective against it. If you predict them doing it, do a quick fair it'll hit before the nair hitbox comes out. Thing is with these moves is that there is a lot of starting lag, but almost no lag at the end of the move so you need to see if you can hit it before it hits you.
An effective way to play against ROB is to jump around the lasers and bite the gyro when far. As you get closer, throw random fairs to clash with their fair or to hit them if they try to nair If you see them using a lot of bairs just keep jumping around near them and hit where they are going to land with a dair or even a fair (even if you land on the ground non-cancelled, just hit them). The thing is, don't challenge the bair!! no point, just don't get hit by it so they don't use it anymore. I played Holy quite a bit, and as long as I don't get hit by his bair he starts to rely more on fair or nair and that is much easier to deal with.
the only thing I hate about nair is that I can't uthrow to uair because it seems to nair hitbox will ALWAYS come out before my uair, don't know how...