The timing is everything. I see many people getting greedy by attempting the fourth hit when Crota just started getting up. They die because of that. You have to keep an eye on his shield while you're up there and try to start hitting Crota right before he even goes down. If timed right then you should be done with your second hit right when Crota hits the ground with his knee. That's how you get four in on him. A failed attempt would lead you to hitting an immune on the fourth and possibly dying from not being invisible or away fast enough. It takes experience to adapt to many teams with different types of firepower each time. I have helped about 60 teams beat Crota as the swordbearer and about 8 of that being from hard mode. And all of that just from 2015. If you're on the Xbox One and need some help, feel free to add me and message me when I'm free. But most importantly keep an eye out on the forums for me. See you around guys. I won't be on for a little because of my constant weasel error codes.