Barreling Down (Horde)

Apparently going from a mount directly onto the barrel can disconnect you. Best to de-mount first.

PSA TO ALL HORDE PLAYERS

If you're wondering why you can't see the barrel to actually do this quest, it's because you cannot complete this quest unless you have previously completed the Legion expac intro quest chain on that character. Else you'll be in the wrong phase for that area outside Orgrimmar.

You can pickup the Legion intro quest chain from the calling board in Orgrimmar. Thankfully you do get a quest skip dialogue option from the NPC outside Orgrimmar that the calling board quest directs you to that ports you to Legion Dalaran and auto-completes it. But the skip option only shows up if you have previously completed the Legion intro quest chain on any other character on your account. So you'll need to port back to Orgrimmar after that and you will then be in the correct phase to see the barrel.

If you've never done the Legion intro quest chain on your account, then you'll have no choice but to do the whole thing first.

Go where the quest marker sends you,
/way 50.49, 13.60 Brew Barrel
Jump on a barrel and roll it on the road, grabbing green speed buffs, avoiding broken barrels along the road and avoiding other rolling barrel obstacles.
Every hit you take reduces your progress by about 35%, so take it safe but do it in one go.
/way 52.61, 40.40 Razor Hill Destination

Tip: Make sure Durotar is not phased, like with Legion intro.