Originally Posted by ReverendSID
Think of it like a TV show. New Episode airs once a week, but once the episode has aired you can watch it over and over again.
From what I read earlier (I forget where) it's not random, it's based on how many people are in the game.
Well, I tried literally about 20/25 times with all four people being there, and all i got was Heroic every single time. Just do it solo, not that hard, just time consuming