I did a search, this method was not found out of the 3 or 4 threads for this achievement.
During the encounter you can right away jump over the ledge in the first room (skip all the fire and frost bombs at the start).
Then during the cutter phase (mario phase) you can skip the first two cutters by running down the right side and jumping on the barrels. Then before the last cutter you stop at the base of the little hill and it wont reach you, but you are under the 2nd to last cutter and can pull the boss there (we have 95% of deaths to the last cutter).
Those are just more of a portion for the guide, but the exploit comes at the end. Everyone mounts up and runs to where the lady is being captured and the worgens will kill her when you get there. At this point you need a warlock or a shaman. The warlock needs to soulstone someone before the the girl dies. Then once everyone is one shot the person soulstoned or the shaman needs to pop up, run to VanCleef pull the boss and everyone gets the achievement.
The reason this is the easiest way to get it now is because previously people could die and take the portal and run up, however this was hotfixed and can't be done. So someone popping up and aggroing the boss still rewards the achievement.