Auchindoun is located in the middle of the Bone Wastes, which is just south east of Shattrath city. You will need to travel East out of Shattrath city and then turn right - or head south, at the first road. Keep following that road until you enter The Bone Wastes.

Travel to the middle of the Bone Wastes and you will find a large, dilapidated stone structure. Auchindoun is located inside these ruins. You will need to work your way through a series of stone corridors before you reach the Summoning Stone for the Auchindoun instances. The Summoning Stone serves the following instances: Mana Tombs, Sethekk Halls, Shadow Labyrinth, and Auchenai Crypts. Mana Tombs can be found by heading directly north from the Summoning Stone.

When you get near the Mana Tombs entrance, you will see many Consortium NPCs where you can acquire several different quests. I recommend you skip all available Consortium quests until you have earned at least Honored Reputation with Consortium by repeatedly completing the Mana Tombs instance.

After you enter Mana Tombs, you will need to successfully pull five or six groups of mobs before you can actually engage the first boss, which is Pandemonius.

Pandemonius has two abilities that all party members should know about:

Void Blast - He will cast a series of five shadow-damage blasts that will also produce a knock-back effect. Since your tank will be positioned with his or her back against a wall or other solid object throughout this entire fight, your tank is going to get hit multiple times in rapid succession from this ability. Your healers must be able to heal him or her through these blasts. For Heroic mode encounters, it is imperative that your tank wear considerable shadow resist gear. Other party members should have 100+ shadow resist gear each (for Heroic mode).

Dark Shell - When this ability is active, you will see a small, green shield (look closely while fighting him; it is difficult to spot). The party leader should immediately tell everyone to stop all DPS when Pandemonius uses Dark Shell. This includes your tank. Spells will be reflected during this time, and melee attackers will take about 1,000 points of damage for every successful hit on Pandemonius. Any damage-over-time-spells (DOTS) cast prior to his casting of Dark Shell will continue to damage him.

Proper positioning:

Near the stone tablet is a mound of dirt that is piled-up against a wall. This mound is one of two spots for tanking the boss. The other position is against the large stone table. Your tank should fight Pandemonius either on top of the mound or with his/her back against the tablet. Melee should position themselves behind the boss throughout this fight and be prepared to move away (if necessary) when he casts Void Blast.

Casters, hunters, and healers should stand near the large, stone tablet and place their back against it. Or, if the tank is positioned against the tablet, the ranged dps/healers should stand on top of the mound. By keeping your backs against the wall or the tablet, you will avoid getting knocked back from Void Blast and avoid missed heals or slowed DPS.

Most newcomers make the mistake of continuing to attack Pandemonius while Dark Shell is in effect. You'll spot these players immediately because they are the first to die, and they will die very quickly. If you're the party leader, it's up to you to let everyone know exactly when to stop DPS.

A simple method to notify everyone to stop DPS is to setup a macro that says, "STOP DPS". You could set it up as a yell or as a warning message that flashes in the middle of the screen. Either way, it's up to the party leader to notify everyone exactly when they should stop attacking Pandemonius. The key to defeating Pandemonius revolves around stopping DPS during Dark Shell. Good luck!