Nightbane is the undead dragon that holds the possible position of final boss within Karazhan, the dispute in general being his difficulty versus that of Prince Malchezaar who is to some considered the true ‘end’ of the dungeon.

Regardless, Nightbane is indeed a formidable foe, possessing two alternating phases and being somewhat reminiscent of Onyxia.  At 75%, 50%, and 25% the boss will enter a ‘flight’ phase and take to the air, forcing the raid to focus elsewhere whilst he slowly descends to the ground once more.

Ground Abilities

Charred Earth – The ground beneath a randomly selected player is ‘charred,’ causing all within the affected area of approximately 5 yards to receive a DoT dealing about 3,000 damage a second, lowered by armor.  This can be avoided by exiting the charred zone.

Bellowing Roar – AoE fear with a 2.5 second cast time and a 30 second cooldown.  This should be hitting all of your melee but in general missing the ranged DPS/healers located at maximum distance.

Distracting Ash – Reduces chance to hit with both melee and spells by 30% for 40 seconds, dispellable.

Smoldering Breath – Deals 3,700 – 4,300 fire damage to all enemies within a frontal cone.  Also adds a DoT dealing 1,688 – 1,912 damage every 3 seconds for a total of 15 seconds.

Tail Sweep – Hits everyone within a cone behind the boss, knocking them back.  Deals 450 fire damage every 3 seconds for a total of 25 seconds.

Cleave – Generic cleave attack, frontal arc, hits quite hard from around 6,000 on more heavily armored targets to above 10,000 on clothies.

Air Abilities

Rain of Bones – This will be cast on a randomly targeted player, bombarding the area around the player with bone fragments dealing around 352-408 damage.  Additionally summons 5 skeletons, each possessing roughly 13,500 health and hitting for a mild 1,000 or so on clothies, lower for higher armor characters.

Smoking Blast – Fired every second for 15 seconds, dealing 1,850 – 2,150 damage, mitigated by armor, and a 3,000 fire damage DoT over 18 seconds.  The DoT part of the attack is dispellable and the physical damage is generally negligible on anything except clothies.
Target of this attack is determined by whoever is highest on the threat meter after he takes flight.

Fireball Barrage – This’ll be cast should any member of the raid be too far away from the boss while he’s in flight, pelts the entire raid with fireballs for about 3,000-3,500 damage and is repeatedly cast until the entire raid is within range.

Positioning

As with the bosses abilities, positioning will be rather similar to your average dragon fight, melee DPS standing at the hind legs on either side to avoid the tail and head attacks.  The tank will have to place himself with back to the wall to avoid allowing the cleave/breath attacks to hit the raid.

Ranged DPS/Healers will be standing at maximum range to avoid the fear and spaced so as to allow easy movement from the area should they be targeted with Charred Earth.

Ground Phase

The ground phase of nightbane is actually quite simple, should your tank be positioned correctly then it resembles a fairly average tank n’ spank style fight.  The major quirk/wipe factor during this stage would be the tank failing to successfully stance dance/otherwise counter the dragon fear.

Admittedly the boss has quite a bit of damage spiking potential should he drop a cleave and smoldering breath on the tank at once, meaning healers have to pay close attention to the tank’s HP despite then relative simplicity of this phase.

The primary difficulty will be mana conservation as the fight runs on into the minutes, making a shadow priest and other mana regeneration aid’s quite helpful.

Flight Phase

Nightbane will engage lift-off, the flight phase beginning and lasting until Nightbane is finished utilizing both Rain of Bones and Smoking blast on the raid.

Begining immediately after the skeletons from Rain of Bones are summoned, Nightbane will target whoever happens to be highest on the threat meter post-flight and spam smoking blast on them, typically this will be a healer as DPS is on the skeletons.

Smoking Blast will deal physical damage and therefore is mitigated by armor, meaning if possible getting the tougher of your healers as the primary target of smoking blast would be favorable.  Paladins would be the best bet, although generally this is not possible, especially due to the priests and shamans possessing AoE high threat heals.

Basically whoever is targeted will need the rest of the healers spamming heals on them to keep them up, making it practically impossible for them to draw attention away and aid the DPS/Tank handling the skeletons summoned.

The skeletons will be handled by having all character at range collapse formation onto the Tank, healers and DPS alike, avoiding any possibility of triggering a fireball barrage and making it easier for the tank to grab the summoned adds.

Feral druid tanks and Warriors will need to spam Cleave/Swipe as well as utilizing Challenging Shout/Roar should they need to hold aggro on the skeletons, Thunderclap and Whirlwind can also come in handy for this.

Hunter Pets are another viable tank for temporary distraction during the initial summoning, but best of all would be the Paladin tank for this situation.  Activating avenging wrath and grabbing hold of all the skeletons makes it quite easy for AoE to move in and annihilate the skeletons as a whole.

Always remember that the healers are occupied and therefore DPS is on its own for the duration of this phase, keeping deaths to a minimum requires careful consideration for destroying the skeletons and staying alive, especially for AoE.

Transition Phase

As it comes time for Nightbane to descend once more you’ll want all members of the raid to begin spreading out to previous positions, Ranged forming groups at maximum distance and melee preparing to flank the boss as before.
The main trouble here will be to have the tank stance-dancing/otherwise ready for fear, an ill-timed fear can wipe the raid while in transition as well as DPS/Healers pulling aggro early on before the tank has established a high threat level.