Noth the Plaguebringer is a friendly fellow just wandering aimlessly in his room. First step to beating this encounter is making sure nobody gets locked out of the room. At the bottom of the stairs, in the doorway to his room, there is a thick black line on the ground (you will know what I am talking about when you see it) and anybody on the wrong side of that line when the encounter begins will be locked out of the room and mocked and laughed at for all eternity. The boss has a relatively small aggro radius so don’t be shy about getting everyone in your raid firmly across the line.
Congratulations! You are now ready to engage the boss. The easiest strategy I have seen involves everyone in the raid grouping up in the center of the room along with the boss. Some adds spawn in the corners and having an offtank (or 2 for the 25man version) ready to pick them up will make everyone’s life easier. By having the whole raid stacked in one place, the OTs should be able to pick up the adds with no trouble at all. The dps ignores the adds and the OTs just sit on them until phase 2.
Every once in a while Noth will blink away from the tank and wipe aggro. The blink was an interesting mechanic in the 40man version because right before he blinked, he would cast an aoe cripple on everyone in melee range, including the tank (He might still cast cripple, but I don’t remember it). So the tank would have a 50% movement speed reduction while trying to pickup the taunt immune boss ASAP following the aggro wipe. At 80 you have warbringer and intervene which would have made the pickup a lot easier, but blizzard went ahead and made the boss tauntable, so the aggro wipe/blink away is a total joke – just be ready to taunt right away and dps can keep trucking along and you really don’t even have to move.
Every two minutes he teleports up to a balcony and becomes untargettable. While he is up there a few waves of adds spawn from the corners of the room. They don’t hit very hard and don’t have a lot of health. If the whole raid is stacked in the center of the room, the tanks will be able to pick up the adds with ease and then you can aoe them down. After about a minute Noth teleports back down and its back to phase 1.
The one “challenging” aspect of this fight is convincing your mages and druids that every 30 seconds or so, they need to stop whatever else they were doing and press their decurse button a few times. Noth casts Curse of the Plaguebringer on 3 random people in the 10man and 10 people in the 25man. The curse has 10second duration and as you can see from the tooltip, if it is not dispelled within 10 seconds, it hits that person and everyone within 30 yards of that person with Wrath of the Plaguebringer which is a very nasty beast. In the 10man, wrath does 4k initial damage and another 1.5k every 2 seconds for 10 seconds and in the 25man it does 6k initial with a 3.5k dot. In the 25man, if one wrath goes off, you are probably going to have a few casualties and if more than one goes off, it is probably a wipe (if you want to wipe in really spectacular fashion, don’t dispel any of the curses and watch the whole raid explode at the same time). Some people have reported that wrath is healable in the 10man if you don’t have any druids or mages in the raid, but I don’t want to test it out…
So, for two minutes your raid pushes their DPS buttons while druids and mages stop to decurse every once in a while and the tank taunts after a blink. Then for one minute the tank picks up adds and they get aoe’d down. Rinse and repeat. Depending on your raid’s dps, Noth may or may not teleport up to the balcony a second or even a third time.