On my first slay Jhen Mohran quest, I was such a newbie because I had no idea what to do since I never fought him before. So my boyfriend just went to damage his arms while I would just do the ballistas and cannons because really, I didn't know what else to do!
However, he got really close and the ship was almost destroyed and I was just bombing him like crazy. And I swear, I managed to stop him five-six times in his attack and literally blasted him out of the sky when he wanted to do his body slam and he would topple over. I thought it was awesome :'D But it was pretty much laughter the entire time because we were so DAMN lucky because that last move of his would destroy the ship, but I managed to halt him every time xD