Hi. As u know near the Morchok spot is a trash with Ancient Water Lord among them. After his death this add remains small pool which gave buff +50% to damage.
So u can kill few trash adds and Bind Elemental Ancient Water Lord (using shaman ability) when this add will have rest of HP around 2%-3% than u pull boss. If its HM u can make same few times from both sides of your 2 camps. After u move Morchok or (Morchok & Kohcrom) u can kill Ancient Water Lord get buff and kill boss much more faster.