I suck at the crucible games but sometimes I have a good game and end up in the Top three. I've never gotten a purple engram int he 30 or so matches I've played. I almost always get a blue engram when I do get something. The other night, though, while playing with a full fire team, I got no rewards in ten straight matches and I was in the top three half the time. The loot is completely random. However, the odds of winning are lower than winning the Powerball Lottery.