Cleaning Up

This is one of the most challenging achievements in the meta, if not the most challenging. 5 minutes is a pretty tight timeline for people who are just gearing up in heroic gear.

To do this achievement, you need to kill the final boss within 5 minutes of killing the Water boss. Obviously, make sure you kill the Lorewalker boss (to the right as you enter) first. After killing the water boss, start sprinting. A few tips:

1. 
   
2. Don't waste any DPS cooldowns on the Wise Mari. Make sure they're all up.
3. 
   
4. After killing the water boss, go towards the entrance and through the middle. It's slightly shorter and will give your tank a better route to pick up all 3 trash packs.
5. 
   
6. Assign one DPS to AoE the trash packs. Demonology Warlocks and Shadow Priests are amazing at this. The other DPS should single-target the three big trash that have a truckload of health.
7. 
   
8. Don't bother killing the three trash mobs before the final boss. Use fear, banish, bind elemental, or simply offtank them. ALL your energy needs to be on the boss
9. 
   

Go fast. This is a tough one!

Seems like it's a speed run achievement (well, for the last two bosses) - 5 minutes to do 4 trash packs and 2 bosses is very, very tight. Unless there's some trick that hasn't yet been seen (like being able to get the water buff after third boss).

Edit: No idea why this was downvoted. Ended up being completely accurate.

You only get the buff in Heroic mode so don't get any crazy ideas about doing this on normal.