User blog comment:Kogath/Monster Hunter Generations Discussion/@comment-6050823-20160614024914/@comment-5569775-20160614231459

Well my personal Theory is that something, possibly Oliver, infected the monsters with a virus that produces an unstable amount of dragon element inside the monsters, which causes them to go berserk. The black mist being parts where the dragon element is condensing and the red flash before attacks from said areas being the dragon element discharging a bit.

Also, I'd have preferred something that made them sound more aggressive, like Ferocious did. But I guess there's no helping it.

@MHAdvent: Yes, it's worse than Astalos, Gammoth and Glavenus, IMHO.