The Lurker Below
If you have imp Vampiric Embrace you can spend the entire boss phases of this fight in the scalding water. Put your Vampiric Touch, ShadowWord: Pain and Vampiric Embrace on the boss at all times and Mind Flay the crap out of it. Since you aren’t running around like a headless chicken trying to avoid the spout etc… you tend to do more dmg this way (I topped the healing meter first time I did this as well ). No need to shield when doing this, imp Vampiric Embrace is enough to keep the scalding water dmg to a minimum, I even do the odd Shadowword:Death as well. Being in the water also makes it easier to stay away from other raid members reducing your chances of being thrown half way across the instance by The Lurker Below knock back attack.
When the boss dives get out the water ASAP since you no longer gain health from Vampiric Embrace. Believe it or not I explained this technique to an ex-guild member and he stayed in the water after The Lurker Below had dived and died due to the scalding water damage!
If you are low on mana and we are killing one of the sheep-able mobs (Guardians I think) send your shadow fiend at it (do it as soon as you can to get max mana back). Try to send it at the back of the add so it doesn’t get cleaved. If you can hold on until the next The Lurker Below phase Wait for The Lurker Below to cast spout and send your Shadow Fiend then. Pets are immune to spout so there’s no risk of it dieing early. You don’t even have to get out of the water to send your Shadow Fiend in, the water doesn’t damage it.
If a sheep breaks and you get aggro bash the fade key and hope for the best, one hit and your dead!
If you die from a spout you’ve either screwed up or been really unlucky when The Lurker Below resurfaces and immediately casts a spout. Got caught once when I stayed a little too long killing a Guardian and as I jumped in the water got hit with an emerging spout (was lucky and survived!).
The knock back and spout seems to be worse if you hit a rock formation behind you (think splat) so try not to stand with one behind you.