While Ultraxion is definitely the most unique fight for healers in this tier, Yor'sahj the Unsleeping is a close second place. The boss' abilities are simple for the DPS classes and tanks, but healers will constantly be reacting to the summoned oozes and their various effects. These globules cause us to shift our healing strategies with each new wave, and learning to handle the globules will be the key to mastering this encounter.
Every raid group is going to handle the ooze packs differently. You need to familiarize yourself with what each ooze can do, and then combine the effects based on your raid leader's preference. You'll be faced with three oozes at a time on Raid Finder and normal difficulties, with the option to kill one ooze out of each wave. On heroic difficulty, there are four oozes per wave, for a total of three effects on the boss after you've killed one of the oozes.
Rest during the ooze summoning
When you look at his native abilities, Yor'sahj is a basic tank-and-spank boss, although he uses a stacking Void Bolt debuff to force your tanks to swap every so often. The real danger comes when he summons a wave of oozes to help him. He calls his oozes every 80 seconds or so and then stands in the center of the room channeling a spell. While your DPS classes run out to pop a globule before it reaches the boss, you should be swinging at the boss for Seal of Insight procs to regain mana. Raid Finder and normal-mode raiders can use Divine Plea or a Potion of Concentration here as well. You have just over 20 seconds before the boss becomes active again.
Don't bother memorizing the confusing globule names, as nobody else will remember them either. The oozes are always referred to by their color, which should be obvious from the bright spew that's released when they're summoned and their own individual coloring. I will be listing the ooze names here for posterity, but you only need to commit the colors to memory.
Spreading out to avoid the green acid
The Acidic Globule's special ability, Digestive Acid, will cause random players to be splashed with acid damage. It's hard to mitigate this damage since it's unaffected by Aura Mastery and we never know who will be targeted next. On Raid Finder difficulty, the damage is simply dealt to a handful of players, and we heal it up. On normal and heroic difficulties, the damage is also spread to anyone within four yards of the target. You'll want to spread out from anyone nearby when there's a green ooze active. Note that you only have to be five yards away to avoid doubling the damage, so don't spread out too far.
Stay close to red, it's warm
The Crimson Globule's special ability, Searing Blood, is basically a Chain Lightning effect that deals damage based on your proximity to the boss. The closer you are, the less damage you take. Any time there's a red ooze active, you want to get as close as possible to the boss. If you're facing a green ooze, you also need to stay spread out. This results in all of the ranged classes forming a tight ring around the boss, with at least five yards between each player. You want to be close to the boss but away from other players.
The above strategy obviously fails in Raid Finder groups due to the lack of coordination, but that's why the green ooze doesn't deal AoE damage in that difficulty. Just have everyone stack up tight on the boss' hitbox, which will greatly reduce the damage you take from Searing Blood. The red/green combination can be deadly on normal and heroic, so be very careful to keep everyone's life topped off.
The yellow ooze calls for Holy Radiance
The Glowing Globule's special ability, Glowing Blood of Shu'ma, lets Yor'sahj's Void Bolts hit everyone in the raid and causes him to cast Void Bolt twice as often. Luckily for us, the split version of Void Bolt doesn't leave a nasty DoT behind. The yellow ooze will also cause him to use his other ooze abilities twice as often, amplifying their effect. You'll find that the yellow ooze is almost always a priority target for this reason. If possible, you'll want for your raid to stack up on top of the boss, and then simply heal through the damage with Holy Radiance. If yellow is paired with a red ooze, then stacking up and AoE healing was already the plan.
When yellow is paired with a green ooze, things can get tough. You want to use AoE heals to bring everyone's life up efficiently and quickly, but you can't stack up on normal or heroic since the acid splashes deal AoE damage themselves. When combined with a red ooze on heroic, this combination can be deadly. The good news is that you can use Aura Mastery to greatly reduce the damage your raid takes, as both Searing Blood and Void Bolt deal magical damage that can be resisted by Resistance Aura.
The Cobalt Globule's special ability, Mana Void, sucks up all of the raid's mana. Every caster in the raid will be left without zero mana, which can make healing difficult. Destroying the Mana Void returns mana to any casters within 30 yards of the void, so stay close to it to ensure you get your mana back. I like to use Divine Plea or Seal of Insight to regenerate some mana right after losing all of mine to the Mana Void, which allows me to heal until we get our mana back. Holy paladins are experts at healing cheaply, so abuse Holy Shock and Word of Glory until the void goes down.
On the heroic version of this encounter, many guilds will opt to leave the first Mana Void alive, which means that you'll be relying on Divine Plea, Arcane Torrent, and any other mana regeneration mechanics you have to carry you through until the next Mana Void is released. Always save your Divine Plea and other mana cooldowns for these phases, as we need to save those CDs for when we need the mana the most. The upside of the blue ooze is that it doesn't actually deal any damage to the raid, so we don't need to be at our full healing capacity anyway.
Holy: Clutch against purple oozes
The Shadowed Globule's special ability, Deep Corruption, makes healing dangerous. Any healing effect cast applies a stack of a debuff onto the target, and when that stack reaches five, the player explodes, dealing massive AoE damage to the raid. Holy Radiance, Light of Dawn, and any of our smaller heals are strictly prohibited for this phase. We can't afford to create stacks of the debuff while only healing our targets for a few thousand life.
The good news is that Beacon of Light and Word of Glory don't actually generate any stacks on our target. If you haven't already put a talent point into Blessed Life this tier, it's about time you moved one over. You'll be using all of your holy power points on Word of Glory, and you'll otherwise be casting Divine Light to keep the tank and raid members alive. You want to use your biggest heals possible here to deal the most healing you can, while watching the debuff and never healing past four stacks. Make sure your raid frame addon clearly shows everyone's current stack count.
It's all about spell efficiently when the purple ooze is active. Most raid leaders will target the purple ooze first in their priority lists for Raid Finder and normal difficulties, so don't worry too much about Deep Corruption unless you're a holy paladin that plans to fight heroic Yor'sahj sometime soon. Purple oozes are also never active with red or yellow oozes, which means the total incoming raid damage won't be incredibly heavy.
The black oozes are easy
The Dark Globule's special ability, Corrupted Minions, allows Yor'sahj to summon a wave of Forgotten Ones adds. Your raid will be cleaving these down, and so there's not much different for holy paladins. You might have to heal up a raid member or two who get hit by them during their fixate, but they're not particularly threatening. Seeing a black ooze in the mix should allow you to take a breath of relief. The DPS will be more concerned with handling the adds efficiently, as Yor'sahj has a very aggressive enrage timer in normal and heroic modes.
The Light and How to Swing It: Holy helps holy paladins become the powerful healers we're destined to be. Find out just how masterful mastery healing can be, gear up with the latest gear, and learn how to PvP as a holy paladin.