Note that Socrethar is extremely weak to all forms of frost, so if your party is without Scryer assistance, a frost mage may make up for this. Chances are you won't be facing the encounter without at least the adds or the debuff, so there shouldn't be much to worry about.
With a half-decent healer and Socrethar's damage nerfed, any cloth wearer should be able to take the hits with ease. With the adds and the debuff, the tanking part is optional. The whole fight itself is a complete tank and spank. He is easily kiteable and affected by CC (like banish & cyclone). Socrethar has fear, knockback, shadow volley and spell reflect shield. Combined with the use of an Aldor's adds, the fight is incredibly easy. When used against Socrethar, this item gives him a debuff that increases all damage done against him by 300% and decreases all damage that he deals by 75%. When a Scryer receives the quest, their quest giver gives them an item called Voren'thal's Presence. Those allied with the Scryers have an equivalent to Deathblow to the Legion called Turning Point. Talk to one of them, and you will start the event that leads up to the final battle with Socrethar. Using this method will successfully spawn the adds that are mentioned in the quest text. The only downside to this method is that you'll have to clear the area around the portal to get to the lair safely. Second, you can use Socrethar's Teleportation Stone, obtained from the Socrethar's Stone quest earlier in the chain.The fight can be difficult without them, unless you have a Scryer helping you that already has the item that gives Socrethar an incredible debuff (mentioned below.) While this is easier in one sense, using this method will find you fighting Socrethar without the help of the adds sent to help you, mentioned in the quest text. First, you can simply use a flying mount and fly up to Socrethar's lair.Socrethar himself is located on a floating island off the northwest corner (36,18) of Netherstorm. The quest, simply put, involves killing a demon named Socrethar (mentioned in a prerequisite quest). However, in the end his will was strong enough to recover from the Legion's corruption and we may find solace in that.Äeathblow to the Legion is a quest for those who chose to ally with the Aldor in Shattrath City, the long questchain starts with Quest:Assist Exarch Orelis. It is an unbearable pity that one so young would fall in battle. Not even my strongest prayer could raise him. The wrath of Socrethar's magic was far too much for young Kaylaan, however. I and the others will recover from our wounds. Orelis and Karja will meet you at Socrethar's Seat I will send Adyen along with them. Take this stone to the Invasion Point: Overlord, between Forge Base: Oblivion and Gehenna and bring your closest, strongest friends with you. Their corruptive powers over mortal souls are such that only the strongest-willed can even stand face to face with them. When facing eredar of great power, large armies are useless for the most part. Performing quests for the Aldor will cause your Scryers reputation to decrease.
High Priestess Ishanah wants you to go to the Legion Teleporter at the northwestern corner of Netherstorm and use it to teleport to Socrethar's Seat.