WoWDB

(IMPORTANT: If doing this achievement with a group, make certain you are stacked on each other for steps 3 and 5.)

Here is a much better way of doing it:

1. Mark the big adds (Servant) as they spawn.
2. Kill the small adds (Minion) if you want, just be careful with your AoE.
3. Kill the last big add to spawn. This will cause Siamat to drop his protective shield and join the fight.
4. Wait for the boss to stop bouncing your character around.
5. Kill the other two big adds.
6. Do you have three stacks of  Lightning Charge? If yes, kill Siamat - if no, wipe and re-attempt the fight.