Before we can engage Azgalor himself we will need to get through the trash waves. Below all the mobs that are in the trash waves are described and explained what they do and how we handle each individual mob. Then a list of wave-setup follows to get a quick overview and feel for how to deal with each wave on its own. After that Azgalor will follow and below you will find a short description of his abilities and how to deal with each one of them. I have added a picture from Bosskillers to the Azgalor part of this guide to give an idea on how to spread out.

Trashmobs on Azgalor

Looking at the waves on Rage Winterchill, Anetheron, Kaz'Rogal and Azgalor theres only a few simple concepts we have to take into account. For the Azgalor fight we will have Giant Infernals and Fel Stalkers joining in. For the mobs I have only listed the abilities that are important to know about during the trash waves.

Ghouls, Abominations and Crypt Fiends
A Hunter kites a Ghoul/Abomination/Crypt Fiend (preferably a Ghoul) towards the NPCs to engage them into the fight, when that is done they kite the mob(s) back through the AoE. The AoE groups consist of Ghouls/Abominations and Crypt Fiends, any class that can AoE will be helping out on these mobs.

Ghoul special ability
Cannibalise - When they go low on health, the Ghouls will run to a corpse and start cannibalizing it, restoring about 7% of their health every 2 seconds, for 10 seconds. If you see a Ghoul cannibalizing, you must stun it or Shackle it or even Fear it as fast as you can to prevent it restoring health. A cannibalizing Ghoul takes an entire raid's worth of DPS to kill.

Abomination special ability
Poison Aura - Sometimes the Abomination will use a poison cloud-like ability, dealing roughly 750 damage to everyone around the Abomination every 3 seconds (basically this is nothing to worry about since only the tanks will get hit and should be healed through).

Crypt Fiend special ability
They will sometimes shoot out tiny spiders at a random person in range. They do about 300-400 damage total. Absolutely nothing to worry about and should just be healed through.

Shadowy Necromancers
A tank picks these up (a DPS Warrior will do), usually there is 1 or 2 alive and kicking so that shouldn't be a problem, anything extra is sheeped/feared. Melee will kill these mobs, it is important that they interrupt their main abilities, which is "Summon Skeletons" and "Shadow Bolt".

Shadowy Necromancer special abilities
Shadow Bolt - A bolt of shadow dealing 2250-2750 to the current target.

Summon Skeletons - Summon a skeleton from a nearby corpse. They can be either a Skeleton Invader, with 32k HP, or a Skeleton Mage with 24k HP. One is a melee type, the other one is a caster. They are no real threat, just an irritation.

Banshees
The Banshees are the mobs to be shackled, depending on the number of mobs we can decide to shackle a few. The Banshees die before the Shadowy Necromancers will, so when there are waves with both the Shadowy Necromancers will be sheeped/feared while melee will focus on the Banshees.

Banshee special abilities
Banshee Curse - Reduces chance to hit by 66% for 5 min. Decurseable.

Banshee Wail - Much like a Shadow Bolt, it causes 2475 to 3025 to the current target.

Anti-Magic Shell - Creates an anti-magic shield around the caster, absorbing up to 200,000 magic damage for 30 seconds. Can be purged.

Gargoyles
The Gargoyles will start in the air, out of melee range. However, if they aggro someone and he goes out of their Gargoyle Strike range, they will land and follow by ground and remain grounded. What we want to do is pull them down to the ground by aggroing them, we can leave this up to 2 Hunters and 2 healers to bring them towards the raid, or we can have all ranged DPS get aggro and move them down to a spot near the Tauren Warriors where they then can be tanked and killed (either AoE or Focus Fire). In both cases melee DPS is taking out the other melee trash.

Gargoyle special ability
Gargoyle Strike - Deals 850 to 1150 nature damage to an enemy. The spell has a 35 yard range and a 1.5 second cast.

Frost Wyrms
They will remain airborne until they die, and so cannot be damaged by melee. They will come in waves 6 and 7 from the direction of the 2 Towers where the tanks and Shadowy Necromancer DPS are. Have him off tanked by a Hunter, Mage or Warlock somewhere away from people, these mobs get killed by ranged DPS.

Frost Wyrm special ability
Frost Breath - A 3 second cast, 35 yard range ability that deals 2550 to 3450 frost damage to it's target and everyone in 8 yards around it, and slowing their movement speed by 50% for 6 seconds.

Giant Infernals
Basically Warlocks are tasked with Crowd Controlling these mobs, they can be banished and feared and should be done so. What we want to do is burn down the NPC tanked Infernals first (as we don't want to lose them) to then release an Infernal 1 by 1. Import is that when one of *our* tanks gets aggro on an Infernal healers should pay attention to the debuff Flame Buffet gives and should dispell it every once in a while.
My guess is we are better off with focussing on the Infernals completely at first so we can give the tank(s) enough time to get the Ghouls under control. After we've dealt with the Infernals we should be able to full out AoE on the Ghouls right before the new wave spawns.

Giant Infernal special abilities
Flame Buffet - Increases fire damage taken by an enemy by 50 for 60 seconds. It stacks infinitely and is cast on the target highest on his aggro list. Can be dispelled.

Immolation Aura - Burns nearby enemies for 414 to 456 fire damage every 3 seconds.

Fel Stalkers
Basically the Felstalkers belong to the first group of AoE'd mobs, together with the Ghouls, Abominations and Cryptfiends they are tanked within the AoE group and burned down. What is really important here is that the Fel Stalkers are not allowed to aggro any mana classes as they will run out of mana really fast, so tanks, makes sure you've got enough aggro on them before calling AoE.

Fel Stalker special ability
Mana Burn - Burns 1140-1260 mana from the Fel Stalker's current target and deals half the mana burned in damage(570-630). Can be interrupted.

Waves on Azgalor

Wave 1 - 6 Abominations, 6 Shadowy Necromancers
Wave 2 - 5 Ghouls, 8 Gargoyles, 1 Frost Wyrm
Wave 3 - 6 Ghouls, 8 Giant Infernals
Wave 4 - 6 Fel Stalkers, 8 Giant Infernals
Wave 5 - 4 Abominations, 6 Fel Stalkers, 4 Shadowy Necromancers
Wave 6 - 8 Shadowy Necromancers, 6 Banshees
Wave 7 - 6 Giant Infernals, 2 Fel Stalkers, 2 Crypt Fiends, 2 Ghouls
Wave 8 - 4 Abominations, 4 Crypt Fiends, 2 Fel Stalkers, 2 Shadowy Necromancers, 4 Banshees

Wave 9 - Boss - Azgalor will come from the normal wave entrance. If you need to slow his approach to allow extra recovery time, a few rogues can chain Distract him. With 3 rogues, you can keep him entirely in place.

Azgalor

HP - 4,200,000
Melee Strength - 7-8k on plate

Cleave
Azgalor's frontal cleave hits for 10,000.

Rain of Fire
Much like the Warlock's Rain of Fire, it rains fire in a 20 yard area, dealing 1619-1881 fire damage every 2 seconds for 10 seconds and applying an undispellable debuff called Unquenchable Flames that deals 1250 fire damage every second for 5 seconds. Used very randomly.

Howl of Azgalor
An AoE silence with a 99 yard radius, that lasts 5 seconds. Used at the very start of the encounter and on a 15-20 second timer after that.

Doom
Cast every 45-50 seconds on a random target, it places a debuff on them called Doom, which after 20 seconds will kill the target. When the target dies, it will spawn a Lesser Doomguard with 62,000 HP on the spot of the dead player, which must be tanked. The ability is not used on the main tank and cannot be removed or avoided in any way by any immunity.

How to deal with each ability
Melee Attacks
7-8k on plate, which is very healing intensive, specially together with the Cleave an unfortunate chain of attacks together with Rain of Fire and Howl of Azgalor can basically 1-shot a tank in seconds.

Cleave
As said above in combination with Azgalors abilities this can be a potentioal tank-killer, healers pay attention!

Rain of Fire
This Rain of Fire is a potential raid-killer and we want to prevent taking damage from it as much as we can. You can outrange the Rain of Fire by standing outside 35y range, anyone who can should! Anyone who can't outrange it should stand at the very edge, and not group up with other people that can't either, this way only one person will get hit by the Rain of Fire.
Melee DPS and Tank(s) will be getting 90% of the Rain of Fire (depending of the amount of people in range), as you can expect healing through the Rain of Fire on tanks is doable, on melee DPS it is not. There are two options to counter this:

• All melee DPS wear 200 FR unbuffed and get a Paladin Aura or a Shaman Totem, melee DPS that don't have any FR gear should not be DPS-ing the boss but the Doomguards.
• All melee DPS will be on the Doomguards and will not be DPS-ing the boss, this is a slight loss in DPS but it adds to the surviveability of the raid and through that healers mana.

Remember that Rain of Fire can be "dispelled" by Divine Shield / Ice Block and Cloak of Shadows.

Whenever a tank gets hit by the Rain of Fire he can just stay where he is, it is however important that healers push out some extra healing at that point, on a tank it is not that much of an extra damage factor though so it should be good.

Howl of Azgalor
And this is where SR comes in, get as much as you can, specially healers, since it is a shadow based spell. Anyone that can resist one of the silences is valuable so try to do so with everything you got. Other than that this is nothing we can do about, however Devine Shield and Ice Block (Cloak of Shadows is not mentioned) will dispell the effect, make use of it!
An important note for healers is to try and top of everyone before the Howl of Azgalor hits, it will minimize any unlucky deaths.

Doom
A nasty debuff, as we will lose people because of it, but easy to deal with. We will assign a spot where the marked person runs to (where Thrall is). The person that gets the debuff runs to the Doomguard tank, who will be roughly positioned at the Tauren Warriors, and stands there until he dies. Two tanks will be positioned there to tank the Lesser Doomguards, 2 healers (or maybe even 1 if possible) can heal these 2 tanks while the NPC's will DPS them down. They should deliver enough DPS to kill the Lesser Doomguards eventually, however at the end of the fight there will be 3-4 Lesser Doomguards up (tanked by the two tanks). After Azgalor dies the raid should finish these off.

Positioning

Important to know that if we position Azgalor and the Lesser Doomguards as in the image below the healers of the Lesser Demon tanks will be out of range of the Howl of Azgalor which makes healing hell of a lot easier.
Another important thing Warlocks should do here is have their Soulstones ready but not used, why you may ask, so we can Soulstone any healers or other important people that get the Doom debuff. This allows them to get ressed and rejoin the fight as soon as possible. Try saving the Soulstones for healers, as they are one of the key players in this fight due to heavy healing.

However after several tries and our first kill we decided to tank Azgalor at Thrall and kill the Doomguards at the Tauren Warriors. The healers for the Tauren Warriors will however get the silence, but due to the Tauren Warrior's Warstomp ability the tanks will need a lot less healing because the Doomguards will get stunned by it.

If we position ourselves as in the image below the MT healers will never ever get RoF, next to that all ranged that has to be within 35y range can stand at a spot where only they will get hit and not all ranged.

Azgalor will come from the normal wave entrance. If you need to slow his approach to allow extra recovery time, a few rogues can chain Distract him. With 3 rogues, you can keep him entirely in place.

Azgalor must be Misdirected as soon as possible to the main tank so that he does not aggro on Thrall or any other NPC's. You don't want the NPCs competing for aggro at the start of the fight.