Immerseus 10 H

First boss in the Siege of Orgrimmar

Quick Facts

Introduction

Immerseus is the opening boss in the Siege of Orgrimmar and, as such, poses little of a challenge. The fight consists of two alternating phases. In Phase 1, you must remove stacks from the boss, kill Sha adds, and reduce the boss's HP to 1. In Phase 2, the boss disappears, splits into multiple blobs, and you must defeat those to reduce his corruption level, his alternative health bar.
Each blob killed or fully healed in Phase 2 permanently reduces the boss’s corruption by 1. At the start of each Phase 1, his health percentage matches his remaining corruption. The boss does not die until the end of Phase 2, once his corruption has been reduced to 0 by a total of 100 blobs that have been dealt with.

As with many bosses, it’s possible to play this fight with three healers during progression. In Phase 2, you won’t need to worry as much about keeping a healer within range at all times then. There are also many healer blobs towards the end of the fight, and for this reason, we recommend three healers for the first few kills of this boss. Later on, you’ll have to decide whether more damage or more healing will result in a faster kill.

You'll probably end up solo-tanking the boss very soon, but for the first kill, it's advisable to use two to be safe. When solo-tanking, your tank will be tanking both the boss and the Sha adds at the same time and should expect to receive two tank debuffs. For the Corrosive Blast ability, the tank will need to turn the boss away from the group.

Positioning

Have the tanks tank the boss at the blue marker and make sure you don't stand there as well during Phase 1, because the frontal, cone-shaped Corrosive Blast is deadly for non-tanks. Position yourselves around the green marker and make sure everyone is within range of the healers. The tank who is not currently active will tank the Congealed Shas in a void-free area near the green marker.
You can step into the channels of shallow water throughout the entire fight; they do not cause any damage.

The goal of each Phase 1 is to reduce the boss's health to 1, thereby triggering Phase 2.

Ability: Sha Bolt

Every ~10 s | Instant | 5 y Splash

About every 10 seconds, Immerseus deals damage to all players and within a 5-yard radius around them, and creates a void beneath them. At the end of Phase 1, all voids move towards Immerseus and disappear. Try to place these voids in a space-saving manner so that the area isn’t completely covered with them. Also spread out within the “section” marked by the green marker so that you don’t cause trouble for other players.

Ability: Swirl

1 x per Phase | 3 s Cast Time | 10 s Duration

Immerseus creates many small voids that, after a short time, toss up any players inside them into the air, dealing some damage in the process. He will then turn to a random direction, fire a Swirl in the direction he is facing, and spin clockwise with it for 10 seconds.

⚠️ Note: Unusual Ability Handling You cannot avoid the Swirl if it starts to the right of the group, as running for too long will cause too much disruption. In this case, it should be countered with individual and group CDs.
If the Swirl starts very close to the right of the group or even right in the group, the group can take a few steps to the right to leave the Swirl that forms shortly thereafter to the left.

💚 Healers You should always have a plan for the Swirl, as it will hit everyone 1–2 times (it “ticks” every 250 ms and deals about 300 k damage each time). You can build up a Spirit Shell as a preventive measure.

Ability: Corrosive Blast

Every ~35 s | 2 s Cast Time | Tank Debuff

The Corrosive Blast deals approximately 900 k shadow damage in a cone-shaped area towards the tank and applies a stackable debuff that increases shadow damage taken and thus subsequent applications by 300 % each.
Note: The tooltip above says 200 %, but that is likely still an error on Wowhead’s part; according to the PTR compendium, it is 300 %.

🛡️ Taunting Tanks should taunt after the other tank has received the debuff or just before the ability is used again. Most of the time, however, you’ll only need to switch tanks at the start of each Phase 1, since due to the increasingly shorter Phase 1 you won’t reach the second Corrosive Blast after about 48 seconds.
Of course, a tank with cooldowns can take a second Blast.

Heroic Ability: Swelling Corruption

1 x per Phase | Instant

Shortly after P1 begins, Immerseus gains the buff Swelling Corruption. The number of buff stacks always corresponds to half of his current corruption. At the start of the fight, this amounts to 50 stacks. As the fight progresses, the boss gains fewer and fewer stacks in Phase 1 due to his decreasing corruption.

To bring Immerseus down to 1 HP, you have no choice but to remove the buff: If you attack Immerseus with single-target special abilities while this buff is active, it decreases by one stack and the player receives a stackable and dispellable six-second debuff that ticks each second.
With each additional stack, the debuff damage increases drastically, so stop your damage to Immerseus after 4 stacks at the latest.

Approximate damage per stack per second:

• 1: 3,000
• 2: 11,000
• 3: 29,000
• 4: 67,000
• 5: 117,000

Priests should make use of Mass Dispel. Combined with individual dispels, you can often completely bypass the damage stop.
Both healers and the add tank should remove a few stacks, too.

Furthermore, every time a stack is reduced, a Congealed Sha spawns that must be tanked. At the start of the fight, there are a lot of adds that should be killed quickly. The adds have approximately 1.3 million health.

🛡️ Off-Tank The off-tank pulls the adds that spawn. It is recommended that a Brewmaster handles this task and uses a cooldown. To do this, the Monk can pick up the first debuff from the boss at the start of the phase, have it taunted off, and then collect the adds.

⚠️ Note: Difference from 25 H In 25-man, the debuff on players can be virtually ignored, since the boss also only has 50 stacks there. Before it can get too high on a player, the ability is already over.
In 10-man, using the same strategy will quickly result in seven or more debuff stacks, and you will die without immunities or dispels.
Back then, it wasn’t uncommon for 25-player raids to kill this boss on nearly their first attempt, while 10-player raids needed 10–20 attempts.

Phase 1: Breakdown

The following is a rough timeline of the abilities during the first Phase 1, i.e. immediately after the fight begins. Because the boss has less health and corruption at the start of each subsequent P1, the sequence is also getting shorter.
The fight is won in Phase 2; Phase 1 is merely a necessary evil.

• 0:05 Spread out across the entire P1. The first voids are starting to form under players. Place them closely to each other.
• 0:10 The boss gains 50 debuff stacks.
• 0:13 The current tank receives the tank debuff - taunt! The former boss tank is now tanking the Sha adds.
• 0:24 The Swirl is about to start. Use healer cooldowns if it reaches the group.
• 0:48 The second Corrosive Blast hits the tank. Depending on your damage to the boss, this may not happen, and the boss proceeds to the second phase.

The boss retreats into the large pool, and blobs start flying to random positions along the edge of the room, which then move relatively quickly towards the pool in the centre of the room. Every blob that is killed or fully healed during this phase reduces the boss's health, corruption, and debuff stacks in all subsequent P1! The boss fight is over when the boss’s corruption is at 0, i.e., when a total of 100 blobs have been dealt with in P2. Then he dies at the end of P2.
At the start of the fight, when the boss still has more corruption, more DPS adds will spawn; later on, more healer adds will spawn.

Phase 2 ends after all remaining adds have reached the pool in the centre.
You can survive his berserk (10 minutes). During berserk, the pool in the centre of Phase 2 turns red and deals extreme damage. However, if the boss were to die after this phase, you can use cooldowns to survive until the phase ends.

Heroic Ability: Sha Pool

Lasts the entire P2

The pool in the centre becomes corrupted, continuously growing and thereby absorbing blobs within a larger radius. It also grows larger when blobs run into it. To reverse the growth, a player must repeatedly stand in for a short time, preferably while using a small cooldown, because it applies a DoT.

🛡️ Tank Task Reduce the pool's size by stepping inside it every now and then. Make sure that the DoT doesn't get too high. It deals 15 k damage per stack.

Add: Sha Puddle (DPS)

Spawn at the Beginning of each P2

The goal is to kill as many of these adds as possible in Phase 2. To do this, DPS should spread out to their pre-assigned positions in the room. Since the room is very large, you can’t just quickly run over to players on the other side. As soon as the adds start spawning, everyone should assess how many adds will land nearby, and position themselves in advance.
Each add killed permanently reduces the boss’s corruption and HP by 1 % at the start of P1.
If an add reaches the pool in the centre of the room, it disappears and deals approximately 90 k damage to the entire raid via Erupting Sha.

The adds can be slowed, rooted, and stunned. If you are within 10 yards of an add when it dies, damage dealt to other adds is increased by 25 % for a short time.

Add: Contaminated Puddles (Healers)

Spawn at the Beginning of each P2

These adds function similarly to the DPS adds, except that they must be healed to full. Fully healed adds do not disappear but continue moving towards the centre.
Healers can really go all out here, since when a blob is fully healed, they regain 75,000 mana within a 10-yard radius of the blob and gain 75 % more healing on blobs for a short time (stackable). So you can heal very intensively even in Phase 1 and replenish your mana here.
The more health these adds have, the slower they move.
Healers should split up on two sides so that all players always have a healer within range, since AoE damage keeps coming in.

Like the DPS blobs, incompletely healed blobs deal approx. 90 k damage upon reaching the pool via Erupting Sha. Fully healed blobs also deal damage: approx. 40 k from Erupting Water.

⚠️ Note: Possible Bug Back then, it often happened that a fully healed blob would stop moving, preventing P2 from ending. You can pull these into the pool using Leap of Faith. After some weeks in the original MoP, however, P1 would automatically continue after a short wait as a bandaid fix for this bug.
You can see this bug in action in our kill video. Shortly after 8:45, our Discipline Priest uses Leap of Faith on an add, and starting at 9:00, you can see how an add comes to a halt next to the yellow world marker and, fortunately, can be pulled into the pool by our Druid using Symbiosis.

Kill Video

This video is our first kill from September 26, 2013, as seen from our Brewmaster's perspective.

Class Tips: Rogue

All damage in this fight is magic damage, so it can be avoided using Cloak of Shadows. The most helpful use is to neutralize the Swirl with it, since your healers will be stressed. Swelling Corruption is not removed, but it does not deal damage while Cloak of Shadows is active and does not gain stacks.
Feint paired with Elusiveness also has great potential, as there are many AoE abilities.

Class Tips: Priest (Discipline)

Think about using Spirit Shell right at the start of the fight; this will allow you to mitigate the initial damage from the voids and the debuffs on the players. Another great opportunity to use it would be before the Swirl, but this doesn’t happen predictably.

During Swelling Corruption, help your raid by removing a few of the boss's debuff stacks by casting a spell on him.

You can use almost as much mana as you want, because if you heal a blob to full in Phase 2 and stand next to it, you'll get 75,000 mana back, plus stackable healing on blobs. To heal many blobs simultaneously towards the end of the fight, use Halo. This is also great as extra absorption/healing for the Swirl. If a blob that hasn’t been fully healed almost reaches the centre, you can pull it back with Leap of Faith or use it to pull a stuck blob into the pool.