The first boss of Icecrown Citadel is preceded by two rooms of trash. These are actually difficult pulls, and entirely capable of wiping a raid if things start to cascade. We can only do it successfully by pulling one group at a time. The Damned are normal melee skeletons that explode and do substantial AoE when they die. Make sure to focus fire them so they don't all go at once. If you pull has any of the nerubians or Servants of the Throne, target them first. The nerubians will web wrap party members (make sure to free healers first!) and the Servants will cast a spell doing frost damage to everyone in a line in front of them. Ranged DPS should spread out perpendicular to them to avoid getting hit by this all at once.
There are also two giant skeletons per room. They only become active once traps are set off. Rogues can see the traps from a short distance and attempt to disarm them. Otherwise, just pull back to the starting chamber with the friendly NPCs in order to reset aggro if you pull them with other trash or ever find yourself in serious trouble. They do a frontal cleave, an AoE interrupt, and a massive amount of melee damage. Fortunately, you'll get a little help from your NPC friends, at least for the first two.
Raid Comp: 2 Tanks, 3 Healers, 5 DPS
Lucky Numbers: Frost Resist Aura/Totem
Then comes Marrowgar, demon of ice, flame, flaming ice, and spinning around like a maniac. Your lucky numbers are: frost resistance aura/totem! With 10 people, we have been 3-healing this. He has no enrage, but has a fair amount of raid damage and a good chance of disabling one healer at a time. Now that he is tauntable and doesn't hit quite so much like a mountain of pain on 10-man, he's rather straightforward. We try to stick to the left half of the room. He'll cleave two targets in front of the him. This should be the tanks. Heal them. He will toss down lines of blue fire (frost damage), but you'll be able to see them coming and should be able to get out with zero or one ticks of damage. Ranged, your priority is getting out of them, not doing dps. He has no enrage.
Marrowgar will also cast Bonespike Graveyard every little while, impaling one player on a spike (generally in the middle of blue fire...life sucks, deal with it). They take quite a bit of damage and the spike needs to be killed quickly by the other dps. We tend to have ranged dps deal with spikes of ranged players, and melee and ranged deal with spikes in melee. Another reason to stick to the left hand side of Marrowgar's room is to make sure that you always stay in range of other dps and healers, in case you get spiked.
Finally, Marrowgar will do a whirlwind (called Bonestorm). He darts around the room, doing mild damage to anyone near him and targeting random players. Run away. Mild will still kill you soon enough, so try not to run away from healers. He'll still be tossing out fire, and it gets less predictable, so watch your footing. If anyone is impaled on a spike, finish with them before running. Ranged should keep hitting him when he's not on top of them. DPS should also use survival cooldowns and potions if they find themselves low on health and on the wrong side of the room for the healers. When Marrowgar comes out of it, he'll have dumped aggro, so tanks should taunt him and then we start again.
Once he's collapsed into a pile of bones, run up the ramp to get to Lady Deathwhisper...
An update from me and closing my guides
5 days ago