Boss Focus: Moroes
In a Nutshell
Moroes, the Tower Steward, is the first non-optional boss in Karazhan. Once he is defeated you will be able to talk to Barnes, the Stage Master, to start the Opera Event.
The fight evolves around crowd control and two tanks competing for top aggro on the boss. For priests, this is a battle that requires you to do a lot of things, continuously, throughout the whole encounter.
Rundown
Moroes comes with 4 (out of 6 possible) adds that are fully crowd-controllable. These composition of adds is re-rolled at each soft-reset (a.k.a. 30 minutes without anyone inside the instance).
The possible adds and their relevant abilities are:
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Baroness Dorothea Millstipe (Shadow Priest)
This is the most dangerous ad, and if present should be killed first. She will not deal much damage and does not need to be tanked. She has a nasty Mana Burn ability, must be interrupted! If not, it will burn nearly all of the mana from the unlucky victim, leaving him/her at low health and no mana left. Not good.
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Lady Catriona Von’Indi (Holy Priest)
Another add that wears cloth and will go down quickly if focused. If you kill any adds before her, make sure she is unable to heal by assigning someone to interrupt her, or crowd-control her in some way. -
Baron Rafe Dreuger (Retribution Paladin)
This add can be quite dangerous if you are not careful. If you are assigned to shackle him, you need to be aware of the fact that he will Hammer of Justice you, the instant he will be freed from his shackles. The best practice is to have a hunter place a Freezing Trap between you and your add. If all goes wrong, you get stunned and he will charge over to pummel you down, he will step into the trap, and you will have ample time to re-shackle him and position yourself properly. -
Lady Keira Berrybuck (Holy Paladin)
This is the add you will shackle first of all. This is because she has the ability to Cleanse her allies, removing Shackle Undead and similar crowd-control effects from them. Be careful to keep her shackled at all times. -
Lord Robin Daris (Arms Warrior)
He can deal quite some damage. Be aware that he will use Mortal Strike on his target. Always try to stay out of melee range of this add, his Whirlwind deals a lot of damage. -
Lord Crispin Ference (Protection Warrior)
This add is not very dangerous. Just control him in some way, because he takes the longest time of all the adds to dispose of. Additionally, stay away from him. If he catches you casting in melee range, you could eat a Shield Bash.
Moroes himself is basically a rogue and uses some abilities that can be tied to class. A key to the fight is his ability to Vanish completely every minute or so, and to reappear shortly afterwards. When doing so, he will Garotte a random member of the raid and return to his previous target. The Garotte is not dispellable by normal means and will last for 5 minutes. Due to this fact, the fight will drain the healer’s mana faster the longer it lasts and speed is the key.
There are a few abilities that can remove the Garotte however: Divine Shield, Blessing of Protection, Ice Block and Stoneform will do the trick. As you can see, dwarven paladins are a nice bunch o’people to have around during this fight. 
Watch out for
Don’t let your shackled add slip your mind. The adds tend to resists quite often and break out of the shackles early, so i would advice you to re-shackle every 10 seconds or so. Keep in mind that re-shackling will not result in less breaks of your shackles. It is mainly a proactive re-shakling in case the mob breaks free and heads towards you. If you want to decrease the resists an breaks, you need to stack spell hit for this fight. It’s a possibility, but the encounter is perfectly doable without it.
If you have a hunter in your raid that has not target to crowd control, ask him to place his Freezing Trap between you and your shackle target. This has saved my cloth clad behind more than once, especially if you are shackling the retribution paladin, that will most likely stun you the second he breaks free.
You also need to be aware of tank transitions when Moroes gouges the current aggro-holder and continues to number 2 on his list of people that deserve some whacking.
Next, if you are tasked to do so, pay attention to those players that have a Garotte debuff going on and heal them when they need it.
If you use your Shadowfiend, always use it the moment when Moroes leaves his Vanish. Else, it may happen, that he will Vanish while your fiend is still active and you lose some ticks of your precccioussssss mana regeneration. *gollum-gollum* 
Healing roles
This fight starts pretty hectic, slows down a bit and continues to build up again. Since there is so much going on, it is best to assign soft roles at best in my opinion. The beginning will see a lot of people taking medium damage, sind some adds will be nuked down fast and Moroes will slice up the tanks. Once all non-permanent crowd-controlled adds are put to their final rest, it’s time to introduce Moroes to the light at the end of tunnel.
At this point there are no, or very few, Garottes are going around, and healing will focus on the tanks mainly. A few Vanishs later things will start to build up, because there will be more and more Garottes ticking away. Finally Moroes will enrage at 30% health. This will increase his damage and attack speed slightly and put an additional strain on the healers.
Overall, you may want to assign one healer to the raid, and one to the tanks. But keep these assignments rather soft, since the fight may run either way.
Rewards
Moroes drops a nice healing off-hand, the Signet of Unshakable Faith. Other than this, you better cross your fingers on your way to the Maiden of Virtue. 
