Zero Tolerance

I've done this about a dozen times and I finally found that the trick is to fight him near the western end of the ramp he's on. If he's on the eastern end, your troll will hit for 300-400 and die horribly. If you pull him to the western end, an event will trigger where Drakmar says "Your disguise doesn't fool me fleshling!" and your troll will start doing 1000+ per hit.

Also be sure to transform a level 76 Servant of Drakuru because the level does effect your troll's stats.

This quest is ok to do, but requires some set up. This is what I've found works.
Go to 30: 49 and

1. Check the area for blightguards - you don't want them disrupting you
2. Refresh your disguise - you don't want it disappearing during the kill
3. Target a Servant of Drakuru (make sure it's level 76) and use your Scepter of Empowerment
4. Use the pet bar to attack Darmuk
5. Spam Feroicious Enrage (first ability) and Gut rip (second ability) when they are up
6. Most importantly don't spam Stunning Force (last ability). Use it only when you see Darmuk turn red. This will mean you stun him during his enrage and should complete the fight with only one pet (tested 5 times).
7. Don't use your own abilities on darmuk or the pet - it will break you out of costume and fail the fight.
8. If for some reason you don't kill him on a single servant, quickly control another servant and immediately use Stunning Force (last ability), you can then run around while your servant kills him, or if you are a class that can kite/in plate, kill him yourself.

Step 1: Make sure your scourge disguise is on!
Step 2: Control a servant.
Step 3: Make sure no phantoms are lurking around where you will be fighting darmuk.
Step 4: Use your servant to fight Darmuk. (DO NOT HELP YOUR SERVANT).

Make sure you use all your abilities on the servant as much as you can during the fight.