None, because I don't play it much, and I don't use stormcaller or hammer (which are by far the two easiest classes for 7th columns). however I have friends that haven't even hit slayers in regular crucible get 7th columns in mayhem. I have had a slayer in mayhem rumble though. You get a super every 30 seconds or less, 3 rounds of heavy and the enemy team has near instant respawn, of course it's the easiest playlist to get a 7th column in. That said, this was a super nice 7th column. I'm not saying it wasn't good, I'm just saying he shouldn't be MORE impressed that it was in mayhem.