1) Clear every single trash mob, kill the first boss.
2) Free Thrall
3) As thrall is running to get his armor go out and kill the 4 mobs by the bridge. If you're a ranged class just nuke them from up high, if you're mellee use any ranged ability to pull them to you.
4) As soon as the 4 mobs in the doorway of the castle spawn nuke them immediately.
5) As soon as all of these are dead jump down and kill the 4 mobs at the end of the bridge and run back to Thrall.
Thrall should be in battle with the last 4 mobs (the second pack in the normal sequence) that spawn at the bottom of the ramp. Let them get him to 25% and then quickly nuke them 1 by one but leaving one to kill Thrall. If you're REALLY skilled you can time it perfectly so you kill the last mob just as Thrall dies, but this has a high chance of failure and if you do fail you have to wait for Thrall to run out of the castle walls and get killed by the second boss which wastes time.
6) As soon as Thrall is dead run back in to his cage inside the castle, wait for the respawn and do all of this again.