Noth the Plaguebringer Tactics

"Behold, Noth the Plaguebringer. Responsible for the creation of the process that distills the souls of the living and places them within the cold cage of undeath, Noth was observed to be refining this process even now." - Commander Eligor Dawnbringer

Noth the Plaguebringer is the easiest boss in Naxxramas, and should be the first boss for any raid just starting off in Northrend, as his trash is used as a basic Test for your raid, and he himself is an easy slay.

ABILITIES
PHASE ONE: Ground Phase
During this phase, Noth will be on the ground, attackable, and fighting the raid himself.

Curse of the Plaguebringer - Places a curse on 3 party members. After 10 seconds, every cursed target will cast Wrath of the Plaguebringer, which will hit everybody in 30 yards range for 3,700 to 4,300 (25 Player: 5,550 to 6,450) Shadow damage and additional 1,313 to 1687 (25 Player: 3,150 to 3,850) Shadow damage every 2 seconds, for 10 seconds.
This curse will just be a warning, really. It's applied to 3 random raid members, and 10 seconds after it's applied, it will switch to a debuff that will deal damage to everyone within 30 yards of the afflicted raid member.
This curse is healable on 10-man, but 25-man is much more dangerous. If you're able to remove curses on 10-man, it should be a priority, but if you aren't, just make sure your healers are on top of it. For 25-man, you should have at least one curse remover if not more.

Cripple - Noth will place a magic debuff on a few players in melee range, reducing their attack speed by 100% and movement speed and Strength by 50%, for 15 seconds.
This is an ignorable debuff that Noth will place on melee targets, making them weaker and slower. If you have a magic debuffer, it might help to get rid of it when it's applied, but it generally will do nothing harmful to the raid in any large amount.

Plagued Warrior - Summoned every 30 seconds while in Phase 1. They Cleave, dealing 110% weapon damage to two targets.
Every 30 seconds in the fight, a skeleton warrior gets summoned into the room. Your Offtank should pick this up and bring it towards Noth. DPS should try to AoE these down, but focus on Noth. If your Offtank is undergeared or underskilled, you should have them call out when they're being overwhelmed by the skeletons, and then have DPS turn to save him.

Blink (25 Player) - Every 20-30 seconds Noth will Blink away from the tank, wiping all aggro and casting Cripple on everybody around his old location.
This ability is ONLY in the 25-man version of Noth the Plaguebringer. It's only real danger is the threat-wipe. You should have someone who can cure magic effects remove Cripple from your tank immediately, and DPS should stop until the Tank can pick Noth back up. If you continue to have problems with this, you can bring a third tank in and have him away from Noth and ready to charge and pick him up when he blinks. Your Offtank may also be capable of doing this, but the Skeletons may cause a problem doing so.

Change Phase: Balcony - After 110 seconds on the ground, Noth will teleport to his balcony, entering Phase 2.
110 seconds after Phase 1, Noth will enter Phase 2.

Berserk - Noth the Plaguebringer will Berserker Enrage after three skeleton phases. This will increase his damage by 1000%.
Self-explanatory, if you take too long to Kill Noth, he'll decide to kill you himself. This is a pretty lengthy timer considering how simple Noth's fight is, so most raids should have no problem with this enrage.

PHASE 2: Balcony phase
During this phase, Noth will be un-attackable and on a balcony in the corner of the room. Skeletons will spawn in a much faster period and will attack the Raid

Phase 2-1 = First Phase 2
Phase 2-2 = Second Phase 2
Phase 2-3 = Third Phase 3

Plagued Champion - Summoned during Phase 2-1 and 2-2. They will use Mortal Strike, dealing 100% weapon damage and reducing healing done by 50% and Shadow Shock, which hits nearby enemies for 2,313 to 2,687 (25 Player: 2,960 to 3,440) Shadow damage.
These will essentially be the same as the Plagued Warriors from Phase 1. A Melee skeleton that hits hard, but in addition to that he will apply a mortal strike effect that will reduce the healing recieved by the target by 50%. They'll also do an AoE attack that deals moderate damage to those around them.

Plagued Guardian - Summoned during Phase 2-2 and 2-3. Their primary damaging ability is Arcane Explosion, which hits every in 30 yards range for 2,313 to 2,687 (25 Player: 2,590 to 3,010) Arcane damage.
These Plagued Guardians only show up in Phase 2-2 and 2-3, but they are a significant danger. They will use their Arcane Explosion often as long as they're alive, and should be prioritized as the first target to die if there are any alive.

Change Phase: Ground - After 70 seconds on the balcony, Noth will teleport back to the ground, re-entering Phase 1.
after 70 seconds in phase 2, Noth will teleport back to the ground and begin phase 1 again. Any Skeletons still alive will have to be killed before DPS focuses back on Noth, as phase 2 skeletons pose more of a threat than Phase 1 skeletons.

STRATEGY
Noth is a simple fight, so any raid attempting Naxxramas should pick him as their first kill.

Your Decursers (if available) should prioritize removing Noth's Curse of the Plaguebringer when it's applied, and healers should be prepared to heal through the spike damage if a curse is missed.

When Cripple is applied to melee targets, any Magic debuffers may remove the effect and free melee. It's helpful, but not at all required to do the fight well.

Your Main Tank should be fighting Noth while your Offtank brings all the adds in phase 1 to Noth, to be AoE'd down. If the Adds overwhelm the Offtank, DPS should try to free the Offtank up by killing off the Skeletons rather than DPSing Noth, but at all other times Noth should be the priority.

When Noth enters Phase 2, priority switches from Noth to skeletons. All DPS should be burning down skeletons as fast as possible, and healers should be prepared to heal DPS and other healers if aggro gets loose. tanks can use AoE Taunts or abilities to maintain control on the Skeletons. Exploding Skeletons should be prioritized as the first kill targets, and when Noth enters phase 1 again, DPS should finish off any of the skeletons from Phase 2 before returning back to DPSing Noth.

Good luck.