Hey, we're in the home stretch now! Sorry for the delay. Real life reared its head and it was hard to get back in the habit of writing.
After beating all four quarters (order doesn't matter) there will be no more trash and the teleport to Sapphiron's lair will open. If you take the boss teleporter after completing the fourth quarter, you will be chain teleported to the main entrance of Naxx and then to Sapphiron's Lair. For future reference, if you die on Sapphiron and can't find your way back to the boss, his teleport is located directly above the entrance to the instance, so when you walk inside, run around and up to get to the platform above you. Run across the green circle and you should teleport to Sapphiron.
Sapphiron is very rough on a new raid group. It seems fairly common that guilds will take three healers because the raid damage is so intense, but two very good healers is doable as well. (My guild's very first 10-man kill only had two healers, one of which was a holy paladin.) This boss is something of a dps race to kill him before the healers run out of mana from healing everyone. More dps makes him die faster, but more healers make it easier to keep the raid alive.
The primary sources of damage to the raid are Sapphiron's constant Frost Aura that ticks for 1200 damage every 2 seconds and a blizzard spell called Chill that randomly wanders around the room. There is also a Life Drain ability that Sapphiron will regularly inflict upon three random members of the raid.
These are the only sources of damage non-tanks should be taking during the first phase of the fight, though being a dragon, Sapphiron unsurprisingly has a Cleave and Tail Sweep attack (the latter of which has a knockback effect) so anyone nearby has to be careful to stay towards the middle of the dragon. A Cleave will one-shot any non-tank, so if for some reason you have to stand close to the dragon, say to avoid a Chill, it's safer to stand closer to the tail around the hind legs.
Because of the constant frost-based damage, it's a good idea for one of the paladins to put up Frost Resistance Aura. Even if you're the only paladin, the frost resist will do more for you than your standard Concentration Aura just because of all the damage it will prevent. While frost resist gear could further reduce damage done to the raid, it's not really necessary. The aura should be enough.
Once Sapphiron is engaged, some guilds will split the raid in half, with half the raid on one side of Sapphiron and half on the other, to minimize the chances of a lot of people being caught in Chill. My guild prefers to keep everyone on one side to make it easier to heal and decurse people (Life Drain is a curse) without worrying about trying to make sure everyone is in range. Especially in 10-man it's possible there will be only one (or even no) decurser present.
Decursing unfortunately can't be done by paladins, but it's worth noting whether or not anyone else in the raid can (mages, druids, and resto shaman). While it is possible to get through the fight without decursing at all, it will be very rough on a two healer group that does not outgear the content; not just because of the additional damage done to the affected players, but because Life Drain will heal Sapphiron and prolong the fight.
As the raid is fighting Sapphiron, the blizzard Chill will travel around the room. It's possible to see it coming, but sometimes people get a little absorbed and find themselves unexpectedly standing in it. This is a fight where it's really important that everyone (except possibly the tank) gets out of the Chill ASAP because the blizzard ticks for 3500-4500 every two seconds. That quickly builds up to a huge amount of damage if three people are standing it and they all take a couple ticks to get out. If I get stuck in it, I will Hand of Freedom myself to remove the slowing effect so I can get out as quickly as possible. If you are focused on tank-healing because you have three healers it might be okay to just heal yourself through it and let Beacon cover either you or the tank (letting the other healers know so they don't panic when your health drops), but if you're raid healing you'll need to move because you'll be taking more damage that you won't necessarily be getting free heals for.
After 45 seconds Sapphiron will fly into the air and shoot an Icebolt at two people that will do 7125-7875 frost damage to them and to anyone near them. The Icebolt will also turn its target into an ice block. If the affected person does not have enough health to survive the Icebolt they will die without leaving an ice block behind, which could be a huge liability when Sapphiron does his Frost Breath attack.
Once he's done with his Icebolts he will begin to cast Frost Breath, which is distinguished by the big sphere of ice that descends through the middle of the room and the emote "Sapphiron takes in a deep breath." Anyone caught unprotected by a Frost Breath will be one-shotted, and the raid has just a few seconds to duck for cover by hiding behind an ice block. If you're not sure if you're really protected, try to judge Sapphiron from behind your ice block. If you get an error that you're out of line of sight, then you're protected.
Also worthy of note is the fact that Sapphiron does not shoot his Icebolts simultaneously, so it's possible for one person to turn into an ice block and have people cluster up behind him, only to have a second person get Icebolted and then nuke everyone clumped around them. The raid should spread out when Sapphiron flies into the air and stay spread out until both ice blocks are up. People shouldn't be all over the room, but 10 yards from the nearest person is fine.
People stuck inside an ice block won't take any damage while they're in there, but it's not possible to heal them either, so if they're low on health, be ready to heal them the instant the ice block disappears so they won't be killed by the next tick or two of Sapphiron's Frost Aura.
After the Frost Breath, Sapphiron will land and Phase 1 will start all over again. This pattern will repeat until Sapphiron reaches 10% health, at which point he will skip his air phase.
Though I like to look the raid healing aspect of this fight, Sapphiron does hit the tank pretty hard, so if there are three healers it may be possible that you will be assigned to focus on healing just yourself and the tank, in which case Beacon yourself and heal the tank. If you have two healers, you are going to have to help raid heal. There's no way around it. Beacon the tank and then heal everyone else, giving the tank extra heals when necessary.
Sapphiron is an endurance fight, so don’t be afraid to pot and use Divine Plea should you ever have a moment where healing seems to be under control. I try to Divine Plea when Sapphiron goes into the air because at the very least the tank is no longer taking direct damage and past the initial burst of the Icebolts, a fifth of the raid (the ice blocks) won't be needing healing.
Kel-Thuzad is a three phase fight, and depending on the luck of the draw, it could be an endurance fight as well. We normally do this with two tanks, but a third (a fury warrior, dps DK, or the like) can be helpful for Phase 3. Generally my guild will not want more than two melee dps classes. If we happen to have more, the extra are instructed to sit on standby and not to dps Kel'Thuzad during phase 2 and 3 unless one of the melee dps already on Kel happens to die.
The first phase of Kel'Thuzad involves the raid fighting waves of abominations, skeletons, and banshees for three and a half minutes while Kel'Thuzad himself is invincible. The abominations have a stacking Mortal Wound debuff, so the tanks will typically take turns grabbing abonimations to allow time for the debuff to wear off. The skeletons are easy to kill, but have a nasty AoE Dark Blast that they'll cast once they reach melee range. The banshees have a cone attack Wail of Souls that they also use once they get in melee range that has a knockback.
Because the skeletons and banshees don’t attack until they reach melee range, it's typically up to the ranged classes to kill them before they get too close, and the tanks and the melee work on the abominations. Generally the healing is not that intensive during this phase (unless a skeleton slips through) so I'll help dps the skeleton adds with Exorcism and my judgements.
The party really gets going in Phase 2 when Kel'Thuzad enters the fight.
At this time there are probably a couple adds left that the dps need to take out, and then the raid has to spread out so that no one is standing near each other. For 10-mans, because we have a smaller amount of healers, we will leave the green circle in the center of the room clear for the healers to stand in. Kel'Thuzad will be tanked where he stands, and the dps will spread out to either side of the room. In 25-mans there typically enough healers that it matters less where they stand because the tanks and dps should be in range of someone, but for 10-mans it's important that the healers be able to reach everyone and it's easiest to do that by putting the healers in the middle and having everyone else spread out around them.
Even when you're sharing the green circle with your fellow healer(s) you'll want to keep some distance from each other and stay towards the edges of the circle because of Kel'Thuzad's Detonate Mana ability. Not only does this horrible spell destroy a fair chunk of your mana, but it'll damage anyone standing next to you. It's tolerable to have Detonate Mana cast on you once, maybe even twice, during the fight, but if you're repeatedly targeted (and it's just the luck of the draw if you are) then it can wreck complete havoc on your ability to keep healing. Chug a pot, hit Divine Plea, and pray that the other healer(s) can pick up the slack.
The other reason everyone needs to spread out (and why there should not be more than two melee and the tank on Kel) is Kel'Thuzad's Frost Blast attack, which will randomly freeze anyone other than the main tank and deal 26% of their health in damage over 4 seconds (for a total of 104% of their health). Frost Blast will also hit anyone within 10 yards of the primary target and similarly entomb them.
Because anyone caught by Frost Blast needs to be healed immediately or they will die, it's difficult to deal with one frozen person, let alone two, and that's why we limit melee dps to two people. In 25-mans additional melee can be tolerated because there are more healers, but in 10-mans someone is extremely likely to die if multiple people end up Frost Blasted at the same time, especially if one of them happens to be the main tank.
If I spot the Frost Blast right away (and the affected person's health is high) then I'll wind up a Holy Light since there will be enough time for it to finish casting and heal them before they die. But if they're already down some health or I find my observational skills slow, I'll Holy Shock the frozen person and then use Flash of Light to keep them up (or Holy Light if there's an Infusion of Light proc).
The most important thing is to give the target heals, any heals, to prevent them from dying. They don't need to be healed to full, just enough that they survive. If they were topped off before getting hit, then that's just 5% of their health. Initial speed in healing them matters more than the amount as long as you reach the threshhold of what they immediately need to survive.
If the affected person is another healer, particularly if it's the only other healer, then I'll use my Divine Favor + Holy Shock macro on them to force an Infusion of Light proc and follow with Holy Light. I really don't like the idea of losing the only other healer in the raid and I find this a good way to guarantee their survival since a Holy Shock crit heals for a good amount and the ensuing Holy Light should bring them up to full. If my DF + HS macro is on cooldown, then I may consider burning Lay on Hands rather than risk losing them.
In addition to the Frost Blasts and Detonate mana, Kel'Thuzad has two other abilities that affect the raid. The Shadow Fissure is a red zone that can appear around any individual raid member, including the tank. Once it appears there are just a few seconds before whoever is inside of it is instantly killed. It's possible to avoid death just by stepping out of it, but healers especially are prone to be focused on healing so they sometimes miss getting out of the Shadow Fissures. You'll have to stay alert for these and be sure to move as soon as you see you're in one.
The other ability that can hit non-tanks is Kel's only raid-wide attack; an instant Frostbolt that hits everyone in the room for about 4500-5500 and reduces their movement speed for 4 seconds. There is a different Frostbolt with a 2 second cast time that will hit the main tank for about 10-13k unresisted damage. The single target Frostbolt can be interupted by various interupt abilities (Counterspell, Kick, etc.) and should be at every opportunity, but if interrupts are low, healing the main tank will become more intense.
At 45% health Kel'Thuzad goes into Phase 3, at which point two Guardian of Icecrown adds will appear from alcoves on either side of Kel'Thuzad's throne. The off-tank will have to be quick to pick them up before they go after anyone else, and if the OT if having trouble getting both of them, this is where having a third plate-wearing class (or a cat druid in bear form) can be handy. They don’t hit that hard so non-tanks can still tank them if necessary.
Probably the worst thing that could happen at this point is that the OT will get hit by a Frost Blast, because they can go down incredibly fast if they're taking 104% of their health in damage on top of having adds on them. It's possible to save an OT even if that happens, but you and the other healer will really have to be on top of things since the OT will need big heals and fast.
If most of the raid is still up at this point, mana pools are reasonably strong, and the OT is not in danger of dying, then the rest of the fight should just be a matter of time.
Because of the Frost Blasts and the large need to help raid heal, I tend to Beacon the MT and then spot heal him as necessary.
Since I started this guide my paladin has been on several more Naxx 10 runs. Healing with 1400 spellpower was surprisingly not that much harder than with 1800. The biggest issue as a barely 80 healer was probably my mana pool but even then, it's possible to survive a fantastically long time with strategic use of Divine Plea. The worst fight for me at 1400 was Patchwerk, since we did that with only two healers and the other healer was also fairly new to raiding. Most fights though will have a few seconds of downtime long enough for you to get most, if not all, of your Divine Plea usage without need to maximize your heals. You just need to time it right.
Worse comes to worst, cancel the buff and/or chug a pot. Don't forget that using Avenging Wrath in conjunction with Divine Plea will briefly reduce DP to the old 20% penalty and that using Divine Illumination any time you expect to be spamming Holy Lights is helpful. If you don't know what your healing will look like yet, just use Divine Illumination every cooldown. Better a little mana saved than none at all.
And the nice thing about being a holy paladin in a 10-man? Chances are every single piece of spellpower plate is going to you uncontested. =)
Healing 10-man Naxx Overview - Part 1 - Arachnid Quarter
Healing 10-man Naxx Overview - Part 2 - Plague Quarter
Healing 10-man Naxx Overview - Part 3 - Military Quarter
Healing 10-man Naxx Overview - Part 4 - Construct Quarter