I've never actually seen Rathian defeated, either offline or on. It's gotten to be superstitious. Any group i'm with, no matter how good otherwise, seems to fall to pieces against Rathian, and we'll fail whether it's my fault or not.
Offline, it's nightmarish. There is no safe way to attack her, and there is no weapon set that can hit more than iher legs (or if there is i haven't found it or unlocked it), unless you're suicidal enough to stand in front of her.
Monster Hunter: pissing me off since 2010.