OK UPDATE
theres footage of the fight on youtube cuz its out in japan now, so if u want to spoil it go there, its not what u think it is!!!
another thing:
apparently the ancient civilization had to sacrifice hundreds of elder dragons to create this robo dragon thing because "In order to make a new life form, another creature would have to lose its life. " The elder dragons were tired of being treated like cattle and declared war on the civilization (elder dragons are sentient!?), which resulted in many dragons dying (hence why elder dragons are so rare now) and the ancient civilization being gone for good. A black fatalis was said to be involved in the war, and destroyed Castle Schrade, and then is rumored to have become a White Fatalis.
wait hold up, Castle Schrade? That's the place you go to in the first monster hunter game! and what do yo fight there? A black fatalis! However, if I recall correctly, theres a chance to repel the dragon instead of killing it. Later on in the next game, what do you fight? A mysterious fatalis that has moved to the volcano for unknown reasons, it's now a red fatalis, but you can see traces of black still on it. Again, I think you can repel it instead of killing it. Finally in MHFU, you go to the Tower (ruins of the ancient civilization) and what is waiting for you? An angry white fatalis, which is literally said to hate humanity.
Maybe it was the same dragon all along, unable to find peace and under constant pursuit by hunters (aka your hunter in all the games). Even after the war, it can never escape humanity.
which brings the question, who's the real monster here? :*(