VIDEO: https://www.youtube.com/watch?v=gp7tPUwvJoM
Nightbane is a 10 Man raid encounter in Karazhan.
Required Preparations
For the tank, a Flask of the Titans or greater is required, along with Stoneshield Potions. The majority of damage put out by Nightbane is physical, so any way to mitigate it is important. As you most definitely want to burn down Nightbane as quickly as possible, bring any pots to increase DPS (such as agility for rogues), and mana pots for your healers. They WILL need it.
Raid Composition
Ideally, you'll want one tank with exceptional defense and hitpoints. Nightbane will focus on this tank while on the ground. A secondary warrior with Improved Thunderclap and Improved Demoralizing Shout is also handy for providing DPS, but not required, especially if your tank owns a Thunderfury. A hunter is also required for correctly aggroing Nightbane when he lands.
At least 5 healers. Constant small healing is ideal, which does provide an edge in taking priests and paladins over druids, as those classes both posses Flash Heal type spells. If you are alliance, a dwarf or draenai priest will also make this fight considerably easier through use of Fear Ward.
Paladins are best off using Fire Resistance Aura on healers or DPS, while the paladin in the tanking group should use Devotion Aura for the added armor.
Shamans are best off dropping totems to aid DPS or Mana Spring totems, depending on who they are grouped with.
Abilities
Phase 1
AoE Fear - The ground will shake shortly before the fear. Easily avoidable on the tank using Fear Ward (for Alliance) or Will of the Forsaken (for undead tanks). If neither of these two options are available, the tank will need to stance dance once the ground shaking animation begins.
Cleave - Does around 7k melee damage on a well geared tank.
Smoldering Breath - Inflicts 3700 to 4300 fire damage to enemies in a cone in front of the caster. While this flame cone should only hit the tank, it will also ignite a random area of earth around Nightbane, which deals 2188 to 2812 fire damage every 3 seconds to those standing on it. If you see the ground change, simply move off it. This Charred Earth will not appear under the tank, so there is no need to move Nightbane.
Distracting Ash - Nightbane randomly casts a debuff on a single person, lowering the range of their spells and abilities by 50%. Not a potential threat until phase 2.
Phase 2
Searing Cinders - 465 every 3 seconds for 18 seconds, stacks up to 4 times. Nightbane will put this on many people. It can be removed with Dispel Magic, but that is not advisable, as he just uses it too often.
Smoking Blast - Nightbane's most powerful ability. Deals 4255 to 4945 physical damage to the target and additional fire damage over time. Once Nightbane targets you with this attack, he will cast it on your repeatedly until you are dead. He can target multiple people with it.
Bone Rain - Nightbane will only use this ability during the beginning of phase 2. Targets a random member of the raid, and spawns up to 6 skeletons adds. These skeletons melee attack for about 600 - 700 on plate.
Fireball Barrage - Throws fireballs at any enemies farther than 40 yards away. 2550-3450 fire damage, rapid chain cast fireballs. Seems to be more an exploit blocker than an active ability. Basically, don't get too far away from Nightbane.
Strategy
Before starting, locate the small lone skull on the ground, this is where Nightbane will always land. Your tank should face the skull, with their back against the edge of the balcony. Healers and DPS should split up equally to either side of the tank, though some distance away.
Raid Positioning for Nightbane
Phase 1
Once Nightbane is summoned, he will touch down in front of the tank. Allow the tank a few Sunders to build hate, then begin DPS-ing Nightbane down. Healers need to chain heal the tank, as he will be taking a considerably large amount of damage. Use of Stoneshield Potions by the tank is extremely advisable.
Melee DPS should position themselves near Nightbane's back legs to avoid cleaves. Going further back will put them in danger of being hit by Nightbane's tail.
Avoid the Smoldering Earth when it appears. As a healer or ranged DPS, you can easily avoid fears by moving out of healing range of the tank, then quickly back in to continue healing.
Once Nightbane has lost 25% of his life, he will fly into the air, and phase 2 will begin.
Nightbane attacking from the air
Phase 2
Phase 2 occurs at 25%, 50%, and 75% health. While Nightbane remains attackable during this phase, it is not suggested. Survival is the main priority. Position isn't as important as it was in phase 1, mainly try to keep within range of your healers. Phase 2 lasts 45 to 60 seconds.
Early in this phase, Nightbane will use Bone Rain to spawn 6 skeleton adds near a player. Crowd control these adds using Frost Nova and Shackle, and kill them off quickly. Don't allow DPS classes to do anything but kill skeletons during Phase 2, as attacking Nightbane may draw aggro when he lands (see below).
Receiving Blessing of Protection after a Smoking Blast (or even before if you're lucky enough) will prevent Nightbane from using additional Smoking Blasts on that target, thereby keeping them alive. The dot attached to Smoking Blast should be removed with Dispel Magic.
One of the biggest challenges of the Nightbane encounter is getting Nightbane to aggro onto your main tank after phase 2. Nightbane wipes aggro in the air, and can land and immediately aggro on to a healer from healing aggro. To combat this, get a hunter to use Misdirection on your main tank and generate as much aggro as possible just before Nightbane lands. Also make sure you have all healers buffed with Blessing of Salvation, and if possible stop healing before the phase transition. It also can help to have your highest aggro healer move near to the main tank.
After roughly a minute, Nightbane will return to the ground, and phase 1 will begin again and the entire process will repeat. During each phase 1, if your DPS is high enough and healers are able to keep the tank healed while not expending all their mana, you will win.