Aran

Trash Mobs:
After Curator there is a set of two sentinels that guard the areas next room although they do not have to be pulled. You can avoid them by pathing along the left side hugging the wall. Do not do so before pulling a sentinel patrol that comes up and down that side however.

Beyond the sentinel are groups of leeches and sentinels. It is advisable to pull the sentinels apart as they patrol back and forth towards you whenever possible and grab the groups of leeches whenever you can by pulling them back to the stairway when necessary. The leeches are interesting in the sense that they are immune to all magic, so casters might feel a little useless here. Level up that dagger skill.

A pathway needs to be cleared to the ramp that rises above the raid to the left when you are below the two sentinels that had been left behind. There is a mob to talk to in regards to the kara quest chain in this area that would require some additional pulls as well if some individuals are at that part. In addition, the raid can find books on the ground that apply a buff for an hour when read. These can be useful and usually saved until Aran or a similar situation (they disappear in inventory when logged off).

After passing up the ramp to the left you will be faced with a circular room that will require clearing. The room contains groups of elementals and single undead elite pulls. It is best to cc as many elementals as you can and take them down one at a time (fear/trap/banish). The undead elite is pretty straight forward.

Through the other side of the room there are two groups of mobs to contend with. One is a group of demons and their summoners, where nothing can be cced. A warlock can enslave and banish while the raid focuses on individual mobs to take down. The other groups of mobs that will be encounterd are phasing undead mobs. They should be marked as they appear, usually groups of approximately 4 mobs. When they reappear you should pull them so that those ccing(shackle/trap) will have time to react and get their cc up.

Before reaching the room to Aran, the raid will pass a bookcase that would lead the raid to Illhoof as an optional choice. Up a small ramp to a door is where Aran will be found and if desired the raid can continue down the hall and skip Aran while heading towards the chess event and the remainder of the bosses; Netherspite and Prince.

Leeches
Difficulty: 5-6 non-elites, minimal damage.
Special Abilities: Immune to magic, melee.
Strategies: Since they are immune to magic, the fights can be considerably frustrating if there is little to no melee dps in the raid, and healers become secondary targets all to quickly for their own liking if damage is not mitigated properly.

Undead Caster
Difficulty: 1 elite, caster.
Special Abilities: Shadow Bolt.
Strategies: These mobs are quite easy to take out and do not require much of anything beyond tanking and dps. If one is pulled on accident with the elemental groups they can be shackled.

Elemental Groups
Difficulty: 3-4 elites, moderate damage.
Special Abilities: Explosion when low on health, melee.
Strategies: CC as many of the mobs at one time you can with banish, traps and fears while the group focuses on a single target at a time. When the elemental reaches a health of around 10 percent he begins a quick countdown where he will explode and do massive damage to surrounding raid members. It has a wide range of explosion. If you stun the mob as he is going into it with hammer of justice or kidney, something of that nature then they will not explode on the raid. Heal the party up after an explosion and proceed to the next target.

Spirits
Difficulty: 4-5 elites, moderate damage.
Special Abilities: Phase shift, melee.
Strategies: The only strategy involved with these creatures is done before the pull. It is relavent for the tank to wait until all the mobs are visable before pullings so that the individuals doing the cc will have time to get their targets. Otherwise the tank will take damage from all four mobs at a time for a short while with loss of healing due to some of the cc's coming from shackles.

Aran::

Aran is arguably the toughest boss within karazhan to master for a raid. It is different from the standard tanking and dpsing segment of normal boss fights. Aran has no aggro list, so there is no reason to build or worry about taking aggro from him. Aran will cast numerous spells throughout the fight and success of his defeat will rely upon every raid member cooperating with one another. One disaster will lead to another which will ultimately lead to the failure of the raid.

Interrupts are an important focal point for this encounter. Aran's spell list is that of a mage (a mage on crack) with certain spells that need to be continuosly countered as he casts them. The following spell list is as follows with a description of each spell preceding the list:

1. Fireball - Standard.
2. Pyroblast - Casted after a mass polymorph on a single target.
3. Frostbolt - Standard.
4. Arcane Missiles - Standard.
5. Arcane Explosion - Casted after summoning the raid to him and Mass Slow.
6. Blizzard - Cast in one edge of the circular room and then moves clockwise.
7. Mass Polymorph - Cast when his mana has depleted.
8. Mass Slow - Cast after summoning the raid to him in the center of the room.
9. Summon Water Elementals - Cast when his life reaches 20%.
10. Flame Rift - Randomly casts flame rift on the raid which triggers an explosion on movement.
11. Evocation - Cast after mass polymorph and mana has been depleted.

While everyone must do their part and there are many ways to accomplish the task of destroying Aran, I will follow a successful route and point out areas where other paths could be taken.

All of the spells unless stated above can happen at random intervals throughout the fight. It is best to have at least 2 interrupters on Aran watching over fireballs and frostbolts as he casts them. This is best done with a rogue and a warrior with kick/shieldbash. They will be responsible for interrupting those effects.

The quicker that Aran runs out of mana, the quicker he will polymorph the raid pyroblast and cast a mass explosion on everyone. Ideally it would be best to destroy Aran before he ever runs out of mana. But this is probably unlikely. One tactic is to do little enough dps that when he does run out of mana, your group sustains the polymorph blast and recovers. This prevents the raid from having to deal with a poly blast followed by the summoning of elementals at 20% at the same time which will often result in a wipe for the raid.

However we will go on the assumption of slowing his mana depletion. In order to keep him from going into the polymorph phase too early there are two important things to consider. First of all, arcane missiles should never be interrupted. It should be healed through. When casting arcane missiles, the mana is already wasted as soon as he begins to cast it. This means that interrupting it only speeds up the casting for the next spell and a quicker depletion of mana. The second thing to remember is that when interrupting a fireball or frostbolt, don't do it right away. Wait until the casting bar is nearly completed so that more time has been consumed that he would be using casting another spell.

As the fight progresses your raid must all be aware of when a flame rift is in effect. This occurs when Aran starts glowing in fire and you will most likely see circles of flame on the ground. If anyone moves while these flames are in effect the whole raid will explode into the air and be doomed since the damage is emmense. When combined with Aran's blizzard, this is a difficult position to live through but you are much better off remaining still inside the icy shards in hopes your healers will keep you alive.

When he begins to cast blizzard a small blue shard will drop on one corner of the circular room. If you notice this shard dropped you will know where the blizzard intends to begin within the next few seconds. It will begin there and move in a circular motion around the room until it returns to its position and fades away. It is best to mark a paladin(BoF) in the raid to keep an eye on the blizzard and guide the raid in a circular motion away from it following in its wake or concentrate the whole raid in the center of the room.

At some points during the fight he will summon the whole raid to the center of the room and cast a mass slowing effect on the raid. He will then be able to cast an arcane explosion which will reach out just a little before the edges of the room. You should not have to worry about dispelling people in the raid since there is enough time to slowly move to the edge before the explosion.

When at 20% Aran will summon four water elementals at four equally spaced sections of the circle. It is best to fear/banish these water elementals and take a few down since they will destroy your healers in this phase if they are not managed properly. They will despawn eventually and if your raid can heal through it then that is a choice you can make.

How to video for reference:

Aran: How to fight.