By de Power of de Loa!

Wait for the Hundred Troll Holdout World Quest in Tal'gurub Zuldazar to pop up.
You will see a huge stairs and the [npc=136960] at the very top of the stairs.
There is also 4 totems near the gong and each of them gives you a debuff:

1. 
   
2. [spell=268816]
3. 
   
4. [spell=268873]
5. 
   
6. [spell=268848]
7. 
   
8. [spell=268970]
9. 
   

You get a debuff for 41 seconds.
Take all 4 buffs and use the gong.
Don't run down, mobs will come to you.
The easiest option is to run back and forth refreshing the totems buffs. You don't even need to dps or heal.

By de Power of de Loa! demo: https://www.youtube.com/watch?v=MzKVhmqHnMY

Closest windrider is Scaletrader Post

You can complete this pretty easily, even if you messed up. Get 90/100 trolls, then run away from the area. You can then run back in, grab 4 buffs, kill the remaining 10 and get the achievement.

I suspect what might spoil this achievement is if you get the Earthen Claw totem (radiates damage to hostiles) before you get the other 3 buffs, and you tag a mob and get credit from it when it dies. If this is correct, then when you enter the area, make sure to avoid Earthen Claw until you have all the other 3 buffs first.

The easiest way to avoid Earthen Claw or tagging any mobs might be if you enter the quest area from the direction of Scaletrader Post. If you go up the dirt hill you can get to the gong and the totems around it without passing the stairs or getting close to the trolls.