Bullfango are giant warthogs basically. They are pretty docile when left alone. However, the moment they see you enter their turf, they'll begin hoofing at the ground and snorting, and then they'll do a running charge at your face that sends you flying and is really irritating if you're focusing on a larger boss monster! Even if you leave them alone as you're moving through the area they will still try to charge at you. Thankfully their aim is not precise so if you keep moving they are liable to miss. It can get frustrating if you're delivering an egg though.