Karazhan

Just finished soloing this achievement with a death knight. Full Naxx 25 tanking gear mostly with a couple of Ulduar items, 51/0/20 blood DPS build (I'd imagine blood tank spec would be easier). Skipped Illhoof, Aran, Netherspite and Nightbane.

A few tips and tricks:

General: frost presence, self-heals with Death Strike, Rune Tap (and Death Pact)

The Opera Event can't be Little Riding Hood. You won't have more than a couple of swings at the wolf before he forces you run around the room helpless again. You'll have to wait for a reset.

The Curator is immune to diseases, so stack diseases and heal yourself with Death Strike on the adds he spawns instead. Just nuke him down when he runs out of mana.

Prince Malchezaar is the only really tough one to defeat in order to complete the achievement. He does a considerable amount of melee damage in phase two (60% to 30%), but the real problem is the phase three where you'll have to endure his melee hits, the axes now floating around, Shadow Nova and Shadow Word: Pain - all eventually amplified by 100% by his Amplify Damage debuff. Try to endure the first 5% or so, wait for him to cast his first Shadow Nova and then cast Army of the Dead to spread the debuffs around. They can't taunt Malchezaar though, so he'll still be hitting you while you try to bring him below 10% before all your ghouls are dead from the AOE damage. Have your cooldowns ready for the last 10% and pray you'll kill him before he kills you.

Does Nightbane drop ilevel 125 item ? No, they're ilevel 115. Does he drop 3 badges ? No, he drops only 2. He's only the last boss in the eyes of elitists and wannabe's.

'A Demonic Presence' quest is associated with Prince.

Following up the quote from Tigole i'd assume completion of the quest will activate this achivement.

Quote: http://forums.worldofwarcraft.com/thread.html?topicId=8557074411&sid=2000