I just want to add that if you are still having trouble after doing it Dreadnut12's way which dose work good. You can have 2 using Apollo but just like he mentioned make sure you hit as many executions as possible. Also if there are any objectives take them out as quickly as possible till the next one comes up. I did one this morning with a random both of us were apollo and we went 20 minutes before our health bar drained to fast for us to keep up